Compass Reading

Figure 1. Sighting compass

 

Multiple people have recommended that I write a post about using a compass. I was reluctant to do so at first, for a couple reasons. The main reason is that reading written instructions in a blog is not the best way to learn how to use a compass. The best way to learn how to use a compass is to hold a compass in your hand and figure it out on your own, not read about it online. The other reason is that one of the main purposes of this blog has always been to provide field techs with useful information they are not likely to get from their crew chiefs or university professors (I started this blog with a post about geomorphology because all my former crew chiefs have had a severe lack of understanding about the topic, and when they did try to teach younger field techs about it, all they did was spread misinformation). But most crew chiefs can teach you how to use a compass perfectly well. And it would probably be more effective to have your crew chief teach you in the field, rather than try to learn from this blog post.

But the archaeologists who have recommended that I write a post about compasses are more seasoned than I am, and I still learn new things from them. So I will defer to their judgment and honor their request.

For the uninitiated, let me back up and explain why archaeologists use compasses. Archaeologists survey parcels of land for archaeological sites by following arbitrary transect lines across their survey areas. We use two main survey methods: shovel testing and pedestrian survey. During a pedestrian survey, we walk across the parcel and look for artifacts on the surface. Shovel testing entails that we search for subsurface artifacts by digging small holes at regular intervals and sifting the excavated soil through hardware cloth.

Both methods may require the use of transect lines, especially on relatively flat terrain. During a pedestrian survey, each field technician will follow a transect line across the parcel, and these transect lines will typically be parallel to one another, spaced apart at regular intervals. This means that the technicians are spaced apart from each other, walking in the same direction along imaginary lines. The interval between each transect line varies by state—in my home state of Illinois, pedestrian survey transects must be spaced no more than five meters (16 feet) apart, but in many Western states, such as Nevada and Wyoming, these transects are spaced about 30 meters (100 feet) apart.

In areas that require subsurface testing, such as a forest or pasture, the technicians will place their shovel tests at regular intervals along imaginary transect lines. In Illinois, and many other states, these transects are spaced about 15 meters (50 feet) apart. Western states such as Wyoming and Nevada don’t really have standards for shovel testing transects because archaeologists in those states don’t use shovel testing to find new sites (they only shovel test after the sites have been found).

You don’t always have to use arbitrary transect lines to conduct a survey. On rugged terrain, many archaeologists prefer to conduct landform-based surveys, in which they follow natural features of the landscape. In mountainous areas, I’ve found that it’s much more effective to walk along the ridgetops and look for artifacts there, rather than single-mindedly follow imaginary lines up and down steep slopes and over treacherous cliffs and gullies.

In the field of statistics, a transect-based survey and a landform-based survey correspond to different sampling methods. Setting up arbitrary transect lines across your survey area is an example of systematic sampling. A landform-based survey is an example of judgment sampling.

I prefer judgment sampling, when it’s applicable, and I think it’s important to know how ancient people used the landscape in different ways. I like to inspect arroyos for bison traps, and I often walk along rock faces in search of rockshelters or petroglyph panels. Even when I’m supposed to be part of a transect-based survey, I frequently wander off my transect to walk up an arroyo or follow a rock face, much to the consternation of my crew mates and supervisors. When I’m supervising other archaeologists, I don’t care much about the precision of transect lines myself.

But some landscapes are so flat that a landform-based survey is basically impossible, and you have to follow transects. In these cases, one of the main challenges for any field tech is staying on transect. That’s not always an easy task, given that transects are completely imaginary lines.

There are two ways to follow an arbitrary transect line in the field. The easiest and most effective is to use a GPS receiver to keep your bearings. A Garmin GPS unit can tell you your current UTM coordinates, which makes it easy to follow a transect line, as long as that line is following a cardinal direction. Tablets and smart phones have internal GPS receivers as well, and they can download a variety of navigational apps, such as Avenza. Avenza is the bane of my existence, but it is very useful because it allows you to draw transect lines at weird bearings that don’t follow cardinal directions.

The more traditional method of following a transect line is to use a compass to follow a bearing. This is essential for all archaeologists (and other outdoorspeople) to know how to do. You may not have access to a GPS, or your GPS receiver may end up lost or broken.

Some archaeologists will berate younger field technicians for making errors while reading compasses. I don’t think this is always fair. Some environments are not conducive to following a compass bearing, and it’s not reasonable to expect one person to stay close to an imaginary line over the course of a mile or more. I’ve used a compass to follow transect lines through dense pocosin forest along the North Carolina coastal plain, where I could not see past 20 feet through the foliage in any direction. It was not possible to sight my compass along something in the distance; I was wobbling randomly through the woods. On at least one of my transects, I’m pretty sure I placed my last shovel test far, far away from the transect’s projected endpoint—possibly on the wrong property. I’ve also participated in a survey in the mountains of northeastern Wyoming, where my transect lines were interrupted by steep slopes and sheer cliffs. Fortunately, I was issued a Garmin GPS receiver, which allowed me to end each transect line at the correct spot.

I should also point out that many older archaeologists are not as skilled in orienteering as they would have the younger generations believe. In the old days, before the availability of accurate GPS equipment, archaeologists used compasses and topographic maps to plot sites on maps by hand. They usually plotted these sites in the wrong spot. I’m not saying I could have done a better job; I’m saying that orienteering with nothing but a topo map and compass is very difficult.

To give you an idea of how difficult orienteering is, I want to draw your attention to the boundary between Wyoming, Montana, and South Dakota, not far from where I live. If you zoom in close, you can see that the western boundary of South Dakota is crooked, where Montana meets Wyoming. It is often said that this is due to a surveying error in the 1800s. One team of surveyors was working their way south, and another was moving north, and they were supposed to meet in the middle. But they missed each other by about a mile, so they drew a crooked boundary where they were supposed to meet. I’ve never been able to find a reliable source to prove this story is true, but I think it probably is. I don’t think the surveyors would have made the boundary like that on purpose. And keep in mind that these surveyors were working in teams, and they were probably equipped not only with compasses, but also theodolites and survey chains. Now imagine what it’s like for a field technician, walking alone on a transect line over rugged terrain and through dense vegetation, with only a compass as a guide. That transect line is not going to be perfect.

Figure 2. Survey error along South Dakota's western border

With all that being said, you still need to know how to use a compass, for professional reasons as well as for safety. So let’s get started.

Reading a Compass

Every compass that we use in the field is what is called a sighting compass. To understand how a sighting compass works, imagine you are standing in the middle of a circle, and the circle is divided into 360 degrees. If you are facing magnetic north, your bearing is 360 degrees. If you turn around and face south, your bearing is 180 degrees. East is 90 degrees and west is 270 degrees. Choosing any number out of 360 will allow you to follow any possible bearing, not just the four cardinal directions. For example, a bearing of 210 degrees will send you towards the southwest.

Some models of compass have an azimuth ring that must be manually adjusted and aligned with your magnetic needle.

Look at the compass below. Let’s say you’ve been instructed to follow a bearing of 280 degrees. But right now your compass looks like this:

 

Figure 3. Sighting compass with azimuth ring oriented towards 360 degrees

So the first thing you do is manually rotate the azimuth ring, so that the mark for 280 degrees is aligned with the notch at the top of the mirror:

 

Figure 4. Sighting compass with azimuth ring oriented towards 280 degrees

But the azimuth ring is not aligned with the magnetic needle, which is facing magnetic north. So you must hold the compass out in front of you at arm's length and turn your body until the azimuth ring is aligned with the needle, as such.

 

Figure 5. Sighting compass with azimuth ring oriented towards 280 degrees and aligned with magnetic needle. It can now be used to follow a bearing of 280 degrees in the field.

Now, you can look past the compass and see that the notch at the top of the mirror is aligned with an object in the distance. That object is at a bearing of 280 degrees from you. You can walk towards it so that you stay on your transect line. You are “sighting” off that object. It helps to bend the mirror towards you at a 45 degree angle, so that you can see the azimuth ring and magnetic needle reflected in the mirror while you try to sight off an object in the distance.

Not all environments are suitable for sighting with your compass. Some are vast and featureless, like the rolling plains of western North Dakota. Some are so densely vegetated that you can’t see 20 feet in front of your face. In these environments, you may need to “back-sight”—that is, you may need to orient yourself from something behind you.

That’s why it is often useful to have someone else shovel testing on your transect with you. If you are shovel testing across a featureless landscape, you can back-sight off the person behind you on your transect.

That’s one model of compass. Here’s a cheaper compass that’s easier to use. The degree markings are attached to the magnetic needle, so they all spin together; you don’t need to manually align them. Just hold the compass in front of you and sight along whatever bearing you need to follow. Unfortunately, the design of this compass prohibits you from adjusting for declination.

Figure 6. Sighting compass with azimuth ring attached to magnetic needle

This model of compass includes a magnifying glass rather than a mirror. To read the bearing on the azimuth ring while you have the compass stretched out in front of you, you look through the magnifying glass, as shown below:

Figure 7. Sighting compass with magnifying glass adjusted for reading degree marks.

Compass Declination

Every compass points towards the magnetic north pole, but most maps are oriented towards the “true” north pole. “True north” is a term that refers to the place where the earth spins on its axis. This is not in the same location as “magnetic north,” where the earth’s magnetic field is pointing downwards. The magnetic north pole is constantly moving. When I was born, it was located somewhere in northern Canada, but it has been consistently moving towards Siberia over the past three decades.

The angular disparity between true north and magnetic north is known as “compass declination.” At most locations on the earth’s surface, true north and magnetic north will be located at different angles from where you are standing.

For example, I’m currently writing this in Belle Fourche, South Dakota. The compass declination here is about eight degrees east (technically, about 7.5 degrees east, but I’ve rounded up to eight). That means magnetic north is oriented about eight degrees east of true north, relative to the spot where I’m standing. My compass needle faces magnetic north, so if I want to face true north (towards the earth’s axis), I need to face a bearing that corresponds with 352 degrees on my compass (360 minus 8).

It can be difficult to add or subtract your compass declination all the time, so it’s nice to have a compass that allows you to manually adjust for declination. Take a look at the first compass I showed you. Right now, the red arrow outline is facing directly at the 360 degree mark. This is adjusted for a declination of 0 degrees, in which true north and magnetic north are in line with one another. 

Figure 8. Sighting compass that has not been adjusted for declination

You can use a key to turn this red outline towards eight degrees. Now, when you align this red outline with your magnetic needle, the 360 degree mark on your azimuth ring is actually facing true north.

Figure 9. Sighting compass that has been adjusted for a declination of eight degrees east

How do you know what the compass declination for your area is? You can find your location on an isogonic chart, which is specifically designed for showing compass declinations. You can also find that information online, on a website run by the National Oceanic and Atmospheric Administration.

Using the Right Map

Not all maps are intended to be used for navigation. Different maps use different projections. You cannot perfectly represent the earth’s round surface on a flat sheet of paper, so every two-dimensional map must introduce some distortion. There are different kinds of map projections that distort the earth in different ways, to allow for some technical usages, but not others.

A conformal projection can be used for navigation, because it preserves angular integrity at the expense of areal integrity. It shows locations as being at the correct angle from each other, so you can use a compass bearing to navigate between two points on the map. The angle between any two points should correspond with a compass bearing you can follow in real life, assuming you always adjust for declination. However, these maps do not show units of land as being the correct area. Every variation of Mercator projection is a conformal projection, including the UTM (Universal Transverse Mercator) projections. This includes all the quadrangle maps made by the U.S. Geological Survey. Historically, archaeologists have used these quadrangle maps for their surveys. This is largely because these maps were designed to be used with compasses for navigation.

Figure 10. Conformal projection showing contiguous 48 states. This projection can be used with a compass

An equal area projection shows units as being the correct area, but the angles between points are distorted. If you try to use an equal area map to navigate, you might get lost, especially if you are navigating between points that are far away from each other. Most archaeological surveys take place at a fairly small scale, so you shouldn’t have to worry about this too much.

Figure 11. Equal area projection showing the contiguous 48 states. This projection cannot be used with a compass.

An azimuthal equidistant projection is possibly the least effective projection you can pair with a compass; it won’t work at all. An azimuthal equidistant map shows all points on a map as being the correct distance from a single spot in the center of a map. It cannot show these points as being at the correct bearing from one another, or even from the map’s center. Most people don’t see or use these maps all that often. They are mainly used by radio operators or fire watchtowers.

Figure 12. Azimuthal equidistant projection centered on north pole. All points on map are correct distance from north pole. This projection cannot be used with a compass.

Closing Thoughts

Try to remember that the goal of any archaeological survey is to observe and record real things in the field, not to follow imaginary lines for their own sake. Don’t get too caught up in what is arbitrary, and focus on what is real. There’s no reason to follow a transect line perfectly if you’re missing artifacts or features in the process. And there’s no harm in deviating from your transect line to find something you otherwise would have missed.

Updated on April 9, 2023

Landowner Relations

 

The friends and relatives of archaeologists often ask, “Where do you work?” It’s an honest question, but the “where” varies. Archaeologists who work in cultural resources management (CRM) spend most of their time surveying land for archaeological sites, and as a result, they seldom need to visit the same parcel of land more than a few times. Once the parcel has been surveyed, they move on to another location, and generally have no reason to come back. Some project areas can extend for hundreds of miles, across multiple states. I’ve done professional fieldwork in 21 states myself. People who work in office environments seem to have trouble understanding this, because they go to the same building every day, without much in the way of variation.

If you manage to explain this, another question you might be asked is, “Whose land do you work on?” There is no easy answer to that question either, because it varies. We work on a combination of public land, private land, and Indian reservations. The people who actually own the land where we work are seldom the people who hired us, and this can lead to a lot of unnecessary confusion and hostility. Archaeologists and their clients do not have a good history of maintaining positive relations with the owners of the land parcels we’re supposed to survey. This is partially because field archaeologists do not always understand or appreciate the tension between our clients and the landowners, and also because we do not always understand the damage we might cause to the landowners’ crops or pasturage.

This post has little to do with the science of archaeology, unlike the previous two posts, which discuss the applications of geology and cartography within archaeology. Instead, this post is meant to be purely practical. It’s a guide to the different kinds of land usage in the United States, and how archaeological surveys might affect different plots of land in different ways.

 

Where Archaeologists Work

First, we need to go back to Section 106 of the National Historic Preservation Act (NHPA), which requires archaeological surveys before any kind of ground-disturbing construction activity that might meet one of these criteria:

1. Uses federal funding

2. Requires a federal permit

3. Occurs on federal land

Due to the third criterion, archaeologists often have to survey federal land. This includes all land administered by the U.S. Forest Service, the National Park Service, the U.S. Fish and Wildlife Service, the Bureau of Land Management, the Bureau of Indian Affairs, and all United States military installations, including those located in foreign countries. When it comes to federal land, the “landowners” are the members of the public, whose interests are supposed to be supported by the government officials who administer the land. That is, except for Indian reservations, which are sovereign nations administered by the Bureau of Indian Affairs.

When archaeologists work on federal land, there are no angry landowners to worry about, because as members of the public, we are all the “landowners.” We may have to deal with angry locals who do not believe the land should be public in the first place, and this hostility can lead to violence, but I will deal with that later.

Now, let’s go back to the first two criteria of Section 106 that I mentioned: federal funding and federal permits. Any construction project that uses federal funding or requires a federal permit should be preceded by an archaeological survey, even if that project occurs on private land. Thus, archaeologists often work on private parcels as well. The clients who hire us often do not own the land itself; they have merely negotiated an easement to use a portion of the land.

Pipeline projects are a good example, because they have been a prominent source of employment for archaeologists over the past decade. Pipeline projects often require a permit from the Federal Energy Regulatory Commission (FERC), and because they need a federal permit, they fall under Section 106, and will require an archaeological survey. Large private companies build underground pipelines that transport fossil fuels or carbon dioxide over long distances. These pipeline companies are usually distinct from the oil companies that actually extract petroleum from the earth. Their pipelines can extend for hundreds of miles, crossing both public and private land. When a pipeline company wants to lay pipe through private land, it does not need to buy the land, but it does need to negotiate an easement with the landowner, in order to use a thin corridor of land within the landowner’s property.  

Some landowners are not willing to allow pipelines through their property. In these cases, a government agency may enact “eminent domain,” effectively seizing whatever land is necessary for the pipeline’s construction, and sending law enforcement to ensure that the angry landowners do not disrupt the construction process.

This is important for field archaeologists to know—sometimes, we are surveying land that has been allocated to a private company’s use through eminent domain. This means that the landowner does not want us there, and may resort to violence.

Of course, pipelines are not the only construction projects that fall under Section 106. Transmission lines, cell towers, highway re-routes, bridge replacements, wind farms, and solar plants may all require an archaeological survey prior to construction, either because they use federal money or require a permit from a federal agency. These surveys may cross both public and private land. In many cases, the client responsible for building these infrastructure projects does not actually own the land where the construction takes place, and must try to work with private landowners. Sometimes the client only plans to negotiate a lease or easement to use the land. Sometimes they plan to buy the land outright, but the survey may be underway before the sale is finalized.

The archaeological survey is usually a very small part of the pre-construction process. Often, the landowners will see a small army of civil surveyors, biologists, archaeologists, and architectural historians marching across their property. Usually, the landowners do not understand exactly who these people are or what they are doing. Even worse, the civil surveyors, biologists, archaeologists, and architectural historians may not fully understand how they are damaging the landowners’ crops or pasture, especially if they are unfamiliar with farm life. This can lead to unnecessary confrontations and bad blood.

Many companies hire land agents or “landmen” to communicate with the landowners, in order to prevent these confrontations. There’s no tactful way to say this, but land agents are usually not very bright. Often, they don’t understand what the archaeologists and biologists actually do, so they misinform the landowners, whether intentionally or otherwise. A competent land agent may be the only thing preventing a confused farmer from putting a shotgun in your face, but unfortunately, many land agents fail to bring their “A game” to work, so you may want to brush up on de-escalation tactics yourself.

Furthermore, many landowners do not even farm or graze their own land, and this can complicate issues. Many landowners lease out their farmland to tenant farmers, and the tenant farmer is responsible for planting, harvesting, and (in some cases) selling the crops. In these cases, crop damage threatens the tenant farmer’s livelihood, and if the tenant farmer has not been consulted about the construction project and the various surveys that must occur beforehand, this too may lead to a confrontation.

 

The Pre-Construction Surveys

In the interest of avoiding such conflicts, I’m going to provide a very brief outline of the different kinds of surveyors who may have to visit a parcel of land before a major construction project. I’m going to focus on what these people actually do in the field, and how these activities might adversely affect either farmland or rangeland. This might be useful information for future or current field archaeologists. It might be useful for farmers or ranchers as well, so feel free to show this to any rural landowners you know.

The Civil Surveyors: These are licensed land surveyors who lay out the project area in the field. In other words, they determine the boundaries of the property/easement/lease area in question, and they usually mark the boundaries and/or centerline in the field with stakes. These stakes have to be in exactly the right spot, and licensed surveyors use precise equipment and years of training to ensure their boundaries are correct. For example, if they are surveying for a future pipeline, they usually plant stakes along the centerline of the pipeline corridor. If they are surveying for a future cell tower, they might plant stakes at the corners of the cell pad lease area.

Land surveyors use a type of modern theodolite known as a “total station” to lay out the project area and collect topographic information. A total station has a small computer situated on a tripod, and the computer shoots a laser at a stadia rod in the distance. The laser reflects off the stadia rod, back to the computer. This tells the computer the distance to, direction of, and elevation of the stadia rod. There is usually at least one person operating the total station, and one person holding the stadia rod.

This process requires a clear line of sight between the total station and stadia rod, across the entire survey area. This means that all the high vegetation between the tripod and stadia rod must be cleared, whether that vegetation be brush, woodland, or crops.

I’ve known land surveyors to clear paths through a farmer’s crops while laying stakes for a pipeline corridor. I assume they needed a clear line of sight for their survey equipment, but regardless of the rationale behind their actions, the farmer was very upset. I don’t hear about this happening very often, so I assume that most land surveyors manage to avoid doing this.

The Wetland Surveyors: These are biologists or environmental scientists who define the boundaries of wetland habitats within the project area.

Many members of the public (especially archaeologists) have trouble understanding what a “wetland” is, and do not understand why they are so important to delineate. A wetland is a specific type of habitat in which the soil is waterlogged part of the year, but not necessarily all year round. Biologists identify wetlands by noticing certain types of plants (such as cattails) that can grow in waterlogged soil. The roots of a plant—unlike its leaves—undergo respiration rather than photosynthesis, and they require oxygen, which can be difficult to find in saturated soil. Wetland plants have special adaptations that allow oxygen to be sent into the roots, even when the ground is waterlogged.

Biologists also identify wetlands by digging small holes to see whether the soil is hydric. “Hydric” soil is soil that is waterlogged during part of the growing season, and it often shows signs of redoxification. Basically, this means that the soil has turned gray, with some pockets of ferric oxide staining. Ferric oxide staining is often evident along root channels. Though wetland surveyors often need to dig some holes on a landowner’s property, they don’t need to dig very many. They typically don't need to dig as many as the archaeologists do.

The purpose of the wetland delineation is to protect wetland habitats. Despite the fact that I’m an archaeologist, I will argue until I’m blue in the face that this is much more important than any archaeological survey. Wetlands are among the most important natural resources we have. They remove toxins from the water supply and serve as a buffer against flooding.

The Cultural Resource Surveyors: These professionals fall into two groups—the archaeologists and the architectural historians.

Architectural historians locate standing structures (houses) within the project area and evaluate them to determine whether they are eligible to be placed on the National Register of Historic Places. This usually entails little more than taking photographs of old houses. It’s probably the least destructive part of the pre-construction surveys.

Archaeologists locate archaeological sites within the survey area. An archaeological site is any place with evidence of human activity more than 50 years old. This includes 10,000-year-old Native American lithic scatters, as well as historical farmsteads from the mid twentieth century.

Archaeologists use two main survey methods, and the application of these methods depends entirely on the ground cover:

The first method is pedestrian survey. During a pedestrian survey, the archaeologists walk across the survey area and look for artifacts on the surface of the ground. This is only effective in areas where artifacts might be visible on the ground surface, such as in tilled agricultural fields, or dry mountains or rangeland where the vegetation is sparse.

The other method is known as shovel testing. This entails that the archaeologists dig a series of small holes at regular intervals across the survey area, and sift the excavated soil through hardware cloth. The interval between each shovel test varies by state. They may be 8 meters apart, 15 meters apart, 30 meters apart, or even 100 meters apart. Shovel testing is most effective in places where vegetation covers the ground surface, such as woodland, pasture, or even agricultural fields where the crops have fully grown and covered up the earth.

Thus, you cannot tell a landowner exactly what you will be doing to his or her land, unless you know exactly what the ground cover is. Ground cover varies by season, and by how the land is used. A pasture, hay field, or forest will require shovel testing at all times of year. Pedestrian survey is usually effective in agricultural fields from late fall to early spring, when the ground may be mostly bare, but as the crops grow over the summer, they reduce visibility, and this may make shovel testing necessary.

Generally, shovel testing is more destructive than pedestrian survey, especially if you have to shovel test in somebody’s crops, such as a cotton field or alfalfa field. Not only will you be trampling the crops as you walk through them, but you will also be digging them up, and you will be knocking them down to make space for the sifting screen that you need to use for locating artifacts in the soil. I can guarantee you that no farmer wants to see a team of people digging holes and sifting dirt in the middle of his alfalfa field. If he has not been warned beforehand, he will probably become very angry. Unfortunately, many land agents fail to explain this process beforehand, and as a result, many an angry and bewildered farmer has looked out in shock to see an unexpected gaggle of 20-something kids digging holes in his crops.

To give an idea of how much shovel testing an archaeological survey generally requires, I’ve made a map that shows where all the shovel tests would be located in a 10-acre survey area, if the shovel tests were spaced apart at 15-meter intervals. As you can see, there are 144 shovel tests packed into that 10-acre area. Each shovel test will vary between about 30-50 cm. in diameter. Many states (including Ohio, Pennsylvania, West Virginia, New Hampshire, and Massachusetts) require that a shovel test be at least 50 cm. wide. Of course, this is a negligible sample of the total soil volume—less than a tenth of 1%—but it seems like a lot more after you've been digging all day, and it probably seems like a lot more to an angry farmer as well.

Figure 1. Map of hypothetical 10-acre survey area, with locations of 144 shovel tests at 15-meter intervals

This was only a brief overview of the many proceedings that must occur before some major construction projects. Many farmers may react with hostility to these proceedings, if they were not warned beforehand, or if they never agreed to allow the construction project to occur on their land in the first place.

You need to understand what today’s farmers have been through. Many farmers are fairly old, and lived through the Farm Crisis of the 1980s, during which many landowners lost their farms to bank foreclosures. They watched the rise of Monsanto and its growing monopoly on seeds. Today, cattle farmers and ranchers are currently watching as monopolistic feedlots force small family operations out of the beef market. And of course, farmers and ranchers are watching pipeline companies use eminent domain to force their neighbors to surrender portions of their land. Among some elderly farmers I’ve known, there is a fear—not wholly unfounded—that shady banks and pipeline companies are trying to take their land. When they see teams of civil surveyors, biologists, and archaeologists crossing their land, they associate us with those entities. Whether we like it or not, we represent our clients, and some of our clients are less than ethical in their behavior.

 

Crops and Ground Cover by Region

This next section doesn’t have much to do with archaeology itself, but the conscientious archaeologist should still try to understand what sort of crops he or she might encounter during a Section 106 survey, and how those crops might affect survey methods. More importantly, you may want to understand how your survey methods may affect the crops or pasture.

Ground cover varies by region, as the percentage of land that is used for agriculture diminishes with arid climates, and the types of crops vary with climate as well. The Midwest—where I grew up—is virtually synonymous with farmland, as the majority of available ground is used for corn and soybean production. You may encounter the occasional cow pasture or hay field as well. Meanwhile, farmers in the Deep South often grow cotton and peanuts (or sugarcane and rice in southern Louisiana). As you go west onto the Great Plains, wheat becomes more important, though much of the available land is used for grazing livestock, rather than agriculture. And even farther west, in the Rocky Mountains and the Great Basin, the climate is too dry—and the soil too hard and rocky—for any sort of agriculture. All the available land is used for grazing, timber, or mining.

The Midwest

Farmers in the Midwest mainly grow corn (maize) and soybeans, which they alternate every year. Corn has a higher yield per acre, and thus is more lucrative, even though soybeans provide more money per bushel. Farmers often plant soybeans every other year in order to fix the soil with nitrogen, which is depleted by corn.

Both corn and soybeans are planted in the spring, grow during the summer, and are harvested in the fall. As they grow, they obscure the artifacts on the ground, and thus make pedestrian survey difficult. Fully grown soybeans may cover the ground so extensively that you cannot see any artifacts on the surface. Many archaeologists will try to conduct pedestrian survey through fully grown soybeans anyway, but this is usually ineffective, and arguably unethical. Fully grown corn does not necessarily obscure the artifacts on the ground, because you can often walk between the rows and see artifacts on the surface. But you may inadvertently damage the stalks as you’re walking.

The best time to conduct an archaeological survey across a corn field or soybean field is the period extending from late autumn to early spring—from harvest to planting, when the ground is bare. Not only does the bare earth allow for pedestrian survey (which is faster and easier than shovel testing), but there is no risk of damaging crops during this period.

However, there may be other factors that obscure the artifacts on the ground, even outside the growing season. If the ground has not been tilled, the fallen corn stalks or bean stalks may cover the ground so thoroughly that no artifacts are visible. Many farmers are switching to no-till farming to reduce soil erosion. While this is good for the environment, it makes life more difficult for field archaeologists. In addition, Midwestern weather is unpredictable, especially during the winter. A winter snowstorm may dump a layer of snow that does not melt for weeks. Pedestrian survey is ineffective in the snow. Shovel testing may be used in the snow, until the ground freezes.

Figure 2. Tilled corn field in late March, before the spring planting, in central Illinois. This field is ideal for pedestrian survey; the locations of surface artifacts have been marked with orange pin flags. 

The Deep South

Farmers in the Deep South often alternate between cotton and peanuts in the same way that Midwestern farmers alternate between corn and soybeans. Peanuts replace the soil nutrients that have been depleted by cotton.

In some places, fully grown cotton can be so thick that it makes it impossible to see artifacts on the ground, so shovel testing is necessary. At least, that is my experience in southern Alabama, where the cotton grows tall and thick. In other places, such as west Texas, the cotton does not grow nearly as densely, so pedestrian survey could probably be effective. Wherever you are, the ground will be more visible after the harvest, especially if it is tilled—but many farmers in the Deep South, as in the Midwest, now use no-till farming.

The Great Plains

The western part of the Great Plains has a drier climate than either the Midwest or the South. Thus, wheat is the dominant crop in the western Plains, because it requires less water than corn does.

Much of the wheat grown on the Plains is winter wheat. Winter wheat is planted in the fall, after the summer harvest. The seeds sprout in the fall, then lie dormant over the winter, lying under the snow. During this time, the young sprouts resemble regular grass—after all, wheat is a domesticated grass. When I was much younger, I sometimes mistook young winter wheat for ordinary grass, not realizing it was a crop (in my defense, nobody grows wheat where I grew up). In the spring, the wheat resumes growing, and by late summer or fall, it is tall and ready for the harvest.

Because of the life cycle of winter wheat, there is a very narrow window of opportunity during which you can conduct an archaeological survey in a wheat field without damaging the crops. This is the period after the harvest (summer to early autumn), but before the planting (early to late autumn). Any other time, you will be walking through or digging through the growing wheat. Like most crops, wheat obscures more of the ground as it grows, making pedestrian survey more and more unfeasible.

After the harvest, there may be enough ground visibility to allow for pedestrian survey, but often, the fallen stalks cover the ground so much that you won’t be able to see any artifacts. As always, tillage makes artifacts more visible, but many farmers now use no-till farming.

Much of the available land in the Great Plains is not used for agriculture at all, but has been set aside for grazing. The farther west you go, the less land is used for farming. In areas that are used for grazing, you will probably not see artifacts through the sod, so shovel testing may become necessary.

The Mountain West and Southwest

I’m using the term “Mountain West” to refer to everything from the Rocky Mountains to the Sierra Nevada and the Cascades, including the Great Basin in Nevada and western Utah. Not much of the land in the Mountain West or the Southwest is used for agriculture. Most of it is open rangeland used for grazing livestock. The climate is generally too dry, and the terrain too steep and rocky.

Shovel testing is not a widely used method of archaeological survey in the West. Archaeologists usually conduct pedestrian surveys instead. This is effective wherever the grass is sparse or nonexistent. Due to the lack of shovel testing, and the absence of crops through which archaeologists would have to walk, archaeological surveys in the West are generally not destructive or intrusive at all. You likely won’t cause any harm other than spooking a few horses or cattle.

But archaeologists may cause other problems for private landowners—especially if, ironically enough, we are trying to survey public land. To understand why this happens, you need to understand that archaeologists often need to drive through private land to reach the public parcels they are supposed to survey, and this might bother private landowners, especially if you don’t bother to ask for permission first.

In the West, there is a lot of public land administered by the Bureau of Land Management (BLM). Private parcels and BLM parcels are often arranged in checkerboard patterns, so that you cannot access the BLM parcels without driving through the private parcels. Some archaeologists drive down private ranch roads on the way to BLM parcels, without even realizing they are trespassing. This irritates the ranchers, who maintain the private roads at their own expense, and are generally not fond of trespassers.

You also need to understand that most Western ranchers hate the BLM (and other federal land management agencies such as the Forest Service). They believe the federal government controls too much land, and they resent having to apply for permits to graze on BLM parcels. These ranchers will not be happy to see archaeologists trespass on their land, simply in order to reach BLM parcels that these same ranchers do not believe should exist in the first place.

I mentioned earlier that this sentiment can lead to violence. This was the mindset of the armed men who occupied Malheur National Forest in 2016. If you trespass on private ranch land near any BLM parcel in the Western states, you will encounter men and women who believe that occupation to have been noble and justified.

 

Figure 3. Federal land in Coconino National Forest, Arizona. The sparse vegetation allows for pedestrian survey.

Livestock

Landowners throughout the United States often raise some form of livestock, and it might benefit archaeologists to know more about the livestock they will encounter in the field. I’ve known archaeologists to make glaring mistakes when working on land with livestock. For example, I knew an older archaeologist who once left open the gate to a horse pasture while working on the property, allowing all the horses to escape. This is the sort of mistake that can ruin your month, and possibly ruin your reputation. In fact, if you take nothing else away from this entire blog post, remember this--do not let livestock escape. If you open a gate to a pasture, close it after you’ve gone through.

Horses

I’m sure you already know what a horse is. What you might not understand is how devastating a leg injury might be for a horse. Horses are very heavy animals that stand on light, thin legs with no muscle support. When a horse breaks a leg, the bone often shatters. Furthermore, horses are active animals that are usually unwilling to sit still during the long recovery process, which makes convalescence nearly impossible. For these reasons, a horse with a broken leg usually will not recover. This is why ranchers and farmers have historically euthanized horses with broken legs. Even with advancements in modern veterinary medicine, most horses with broken legs can’t be saved. If your negligence causes a horse to break a leg, the animal will probably be put down.

If there is a second thing you should take away from this blog post, it is this--make sure you completely backfill your holes while shovel testing in a horse pasture! If your shovel test is not filled in correctly, a horse could trip in the hole and break its leg. If the horse breaks its leg, it will probably be euthanized, and you’ve just cost the farmer at least $3000. The horse farmers I’ve encountered have warned us field archaeologists to be extremely cautious about this, and I’ve tried (without success) to explain this to past supervisors, but most archaeologists seem ignorant of the threat they pose while shovel testing in horse pastures.

The best way to backfill a shovel test is to keep your excavated soil on a tarp, and use the tarp to slide the soil back into the hole. But even if you use this method and manage to completely backfill your hole, the backfilled soil will continue to be fairly soft and loose until it settles. I’ve returned to survey areas where I had recently backfilled several shovel tests, and found that deer had been stepping into the backfill during the night. I could see that their narrow legs had been sinking deep into the still-loose backfill. The same could easily happen with a horse or cow. My point is that you can do your best to minimize risk, but sometimes shit happens. Fortunately, the only ungulates on that particular plot of land are whitetail deer; there were no horses or cattle to worry about.

There’s no guarantee that a horse will be clumsy enough to trip and break a leg. It depends on the horse. The feral horses of the Great Basin are perfectly adept at traversing steep, rocky ground without injuring themselves. But a Midwestern farm horse that has spent its entire life in a perfectly flat, stone-less pasture can easily trip and break a leg, especially if being ridden by someone who isn’t paying attention.

Figure 4. Curious horses disrupting a small archaeological excavation in southern Oklahoma

Cattle

Cattle are not as likely to break a limb, and when they do, they usually recover quickly, unlike horses. If a cow breaks a leg, the best advice is to let it lie around all day, which is something most cows are happy to do anyway. That being said, you should still backfill your holes properly in a cow pasture.

On a ranch or cattle farm, the cows are more likely to hurt you than you are to hurt the cows. During calving season, the female cows may charge you to protect their babies. The bulls may charge and kill you any time of year.

Other Livestock 

Farmers and ranchers will raise a variety of other animals, including sheep, goats, ostriches, llamas, alpacas, and bison. I am not familiar enough with most of these animals to know their specific needs, so you may want to communicate with the farmers or ranchers themselves if you find yourself surveying their pastures.

 

Other Land Uses

So far, I’ve mainly discussed crops and livestock, but landowners use their properties for a variety of other purposes, such as hunting, logging, and syrup production.

Many farmers use their land for hunting, and even let other other people hunt there, for a price. Because hunting has become so commercialized in recent years, these farmers may be upset if you disrupt their whitetail habitat, or if you happen to be surveying while they are hunting.

Also, many landowners raise trees for lumber. As an archaeologist, you may find yourself shovel testing in what appears to be a forest, severing roots with your shovel as you dig, without realizing you are actually surveying a tree farm.

One of my old friends lives on a farm that taps maple trees for syrup, which provides a source of income for her family. A pipeline company used eminent domain to cross her family’s land, and the pipeline company’s property assessors failed to realize that these maple trees were used for syrup production, so they underestimated the trees’ value. My friend’s family was never compensated the correct amount for the maple trees that the pipeline company destroyed.

Keep in mind that, when you are working in CRM, you are more than just an archaeologist. You are a point of contact between your client and whomever owns the land that your client wants to use. Your client may not behave with integrity, and as your client’s representative in the field, you may have to bear the brunt of the negative consequences.

It is not lost on me that, with all this talk of land ownership and property easements and eminent domain, and all the disputes inherent in such a topic, we archaeologists are studying the original inhabitants of the land, who were forcibly removed from their homes through a long process of violent genocide. Nor is it lost on me that the descendants of the original inhabitants are still here, and many of them do not want the material possessions of their ancestors disturbed or collected by anyone, archaeologists or otherwise. That is something to think about, wherever you happen to be working on an archaeological survey. While the current landowners may claim not only the land, but all the artifacts on it, the descendants of the people who made those artifacts are still alive, and arguably should have a greater voice in what happens to those artifacts, and how they are interpreted. I did not add this paragraph as a mere afterthought, but I wanted to give younger field techs or anthropology students something to ruminate over before they go on to their next project. We need to have more respect not only for the current landowners, but also the original landowners. Young college students are always the first to claim that they respect Indigenous rights, and yet are often the furthest removed from Indigenous people, with little understanding of the issues that contemporary Native American communities face.

Updated on April 11, 2024

Mapping, GPS, and GIS

 

 Mapping is an essential skill for archaeologists. Archaeology is the study of artifacts within a geographic context, and maps are necessary to provide that context. In the academic world, archaeologists use geographic data to study ancient settlement patterns across the landscape, and theorize about what those patterns might tell us about environmental adaptations, economic relations, or political power.

Mapping also has more practical applications for archaeologists within the CRM (cultural resources management) industry. The purpose of CRM is mainly to locate archaeological sites before they can be damaged by construction. Thus, accurately recording the locations of these sites is one of the most important duties of any CRM archaeologist. You cannot protect an archaeological site from an approaching pipeline or transmission line if you don’t know exactly where the site is.

 

Collecting Geospatial Data in the Field

In the early days of CRM archaeology—before the proliferation of GPS technology—mapping was a challenge. Archaeologists are generally not trained as land surveyors, and they often conduct pedestrian surveys in remote back country wilderness areas. In the old days of CRM, field archaeologists would trek out onto the open rangelands equipped with a compass and topographic map, and use their orienteering skills to plot newly found archaeological sites on their maps by hand.

This was not very precise or accurate. I was not a field archaeologist in the old days, as I did not enter CRM until 2011. But I’ve georeferenced* quite a few archaeological survey maps and site maps from the period prior to the year 2000, back when sites were often plotted by hand on USGS (U.S. Geological Survey) topographic maps. And in some cases, I’ve been able to compare these early maps with newer, more accurate maps that show the precise locations of these sites. On the old maps, archaeological sites are usually plotted in the wrong place, often by quite a wide margin. A good field archaeologist could plot a site on a map within about 40 meters of its correct location, but the plotting of some sites was off by more than 100 meters.

I should add that most of the maps I’ve personally georeferenced were drawn in northern Nevada, which is not an easy place to keep your bearings without modern GPS equipment. Northern Nevada is a sparsely populated desert covered in wide open rangeland, with many areas lacking distinct landforms that might be visible on a standard topographic map. Under these conditions, accurately plotting an archaeological site with no more than a topo map and a compass is extremely difficult. It’s a testament to the skill of the early field archaeologists that they were able to plot sites within about 40 meters of their correct locations.

But today, that level of accuracy is not quite good enough. A field archaeologist who accidentally plots an archaeological site 40 to 100 meters away from its correct location will end up protecting the wrong piece of land from construction, while inadvertently routing a pipeline or other construction project directly through the actual site.

Fortunately, the advent of GPS technology has added both accuracy and precision to our work. When the CRM industry began with the passage of the NHPA in 1966, GPS technology had not even been invented yet. But today, it is an indispensable tool for every archaeologist working in NHPA compliance.

The United States military invented GPS (Global Positioning System) in 1973, though it was not really operational until 1978. The military launched several navigational satellites into orbit, and these satellites now send signals to receivers back on earth. Trilateration of these signals allows a receiver to calculate its exact position on the earth’s surface. And thus, GPS was born.**

GPS technology was not available for civilian use until 1983, and even then, civilian access was restricted by the military’s policy of “selective availablity.” The military scrambled the signals being sent to civilian GPS receivers, ensuring that these receivers could not be accurate within less than 100 meters of the correct location. Selective availability remained in effect until Bill Clinton signed it away in 2000.

After the year 2000, now that civilians had access to much more accurate receivers, civilian use of GPS technology exploded. It became a handy tool for archaeologists and nearly everyone else. I was about eleven at the time, and I remember that this was the period when people who were much wealthier than me began to buy GPS navigation devices for their vehicles.

Twenty years later, the current archaeologist has access to a wide arsenal of GPS technology that can be used to record the real world coordinates of artifacts in the field, and upload those coordinates to a cartographic software program on a computer. The most popular devices (among archaeologists) have traditionally been made by the rival GPS companies Trimble and Garmin, but many archaeologists now use the internal GPS receivers found within their smart phones or tablets.

Garmin produces handheld GPS receivers that are accurate within about 3.65 meters of the real location under ideal circumstances (not accounting for clouds or trees that might obstruct the satellite signals). These devices are widely used in the Western states.

Trimble produces even more accurate devices. Any handheld device within the Trimble GeoExplorer series can be accurate within about 60 cm., or a little over half a meter. These are the devices that I have typically used during my career. A Trimble Juno receiver is accurate within about five meters, making it less popular among archaeologists.

Figure 1. Trimble GeoExplorer GeoXT GPS receiver displaying UTM coordinates collected in the field. This GPS receiver is capable of submeter accuracy.

All of the devices I’ve described so far are handheld devices that can be used on their own, but some companies produce special GPS receivers that can be paired with your personal smart device, such as a smart phone or tablet. The Trimble R1 and Juniper Geode are small GPS receivers that can pair with your smart phone or tablet via Bluetooth, offering submeter accuracy (much like a Trimble GeoExplorer). The internal GPS receiver inside your phone or tablet can't achieve submeter accuracy on its own. When used without an external receiver, your phone's GPS probably won't be accurate within less than about four meters (I've used a special app to test the accuracy of my field phone, and it was consistently accurate within about four meters—or so the app claimed).

If you don't need submeter accuracy, you can use a smart device on its own. A variety of data collection apps can be downloaded on any phone or tablet. One of the most well known is Avenza, but it is not the only one. ESRI has produced a geospatial data collection app known as Field Maps to replace its old app, known as Collector. 

All these devices have strengths and drawbacks. Any handheld device within the Trimble GeoExplorer series should be rugged enough to withstand the rigors of the field, while consistently providing submeter accuracy, but the data you collect is worthless unless it can be exported to a usable file on your computer. At the moment, the only way to do so is with a software called Pathfinder Office, which is very expensive. Garmin handheld devices are also very rugged, and it is cheap and easy to export data from them, but they are not very accurate (by archaeological standards). Smart phones and tablets are neither accurate nor rugged; you'll be lucky to achieve accuracy within four meters, and they are delicate little objects prone to breaking in the field. But you can use them to download a variety of different data collection apps to suit your needs. You can also pair them with a Juniper Geode or Trimble R1 to achieve high accuracy. These external GPS receivers are rugged, but the smart phones and tablets are not, and you can't really use the external receivers without a functioning smart device. Also, it is easy to lose the Bluetooth connection between smart device and external receiver without noticing, and then you end up using your smart device's internal GPS receiver to collect less accurate data than you need.

Also keep in mind that GPS receivers only work when they receive a signal from multiple satellites, and they aren’t effective if something obstructs those signals. Clouds and heavy tree cover can obstruct satellite signals. I once had to climb a tree in the field to get adequate satellite reception.

You can use any of this GPS equipment to collect real world coordinates in the field and upload those coordinates to a cartographic software platform on your computer. The study and usage of cartographic software is known as GIS (Geographic Information Science or Geographic Information Systems). For archaeologists, the most popular GIS software is ArcGIS, which is produced by a company known as ESRI. ArcGIS was originally designed for environmental scientists, but archaeologists frequently use it to process geospatial data and make maps. I was once a GIS technician specializing solely in archaeological data, and I used ArcGIS almost every day.

This is only a basic overview, because the process of uploading data and converting files can be complicated, and this is not meant to be a software tutorial.

 

Entering Geospatial Information Into Official Records

Now that you have a rough idea of how archaeologists record the locations of sites, it might be useful to know how those locations are entered into official records.

Every state in the United States is responsible for keeping records of the archaeological sites that are discovered during CRM surveys. Many states maintain online geospatial databases, where qualified archaeologists can log in and see where all the previously recorded sites have been plotted, as well as which areas have already been surveyed. For example, the state of Nevada maintains a geospatial database known as NVCRIS (Nevada Cultural Resource Information System), and when I was a GIS technician my job was to make corrections to the site boundaries and survey area boundaries within the database. Databases such as NVCRIS are restricted to qualified archaeologists. They are not open to the general public, out of the fear that members of the public might use this information to locate archaeological sites themselves and loot them for valuable artifacts. Looters commonly vandalize rockshelters or Native American graves in pursuit of artifacts that they can sell to collectors.

Before the introduction of geospatial databases, the individual states kept collections of paper maps on which the site boundaries had been drawn by hand. The state of Oklahoma (where I did fieldwork for my Master's thesis) did not have a geospatial database for archaeological sites until the end of 2022. Before then, anyone who wanted to know which sites had already been recorded in Oklahoma had to go to Norman, Oklahoma in person, and go through a collection of topo maps that had archaeological site boundaries drawn over them in pencil.

If you find an archaeological site in the field, you will need to submit your findings to the appropriate state government, and sometimes to a federal agency. Typically, this entails that the site boundary be plotted on a USGS topographic map. Originally, the site boundary would be drawn on the map by hand. Today, this can be done digitally, with ArcGIS or some other computer program. You may also be able to submit your geospatial data directly to the government agency, in the form of an ESRI shapefile.

 

Legal Descriptions

You will also need to fill out a site form. Different states use different formats for their site forms, but any state that uses PLSS (Public Land Survey System) will require geographic information in the form of a legal description.***

A legal description is what land surveyors use to keep track of parcels in their official records. In order to explain how to write a legal description for an archaeological site, I’m going to show you how to write the legal for the abandoned brick grain silo outside the house where I grew up in rural Illinois. I can’t show you the location of a real archaeological site that has been recorded in a database, because that information is confidential. As I’ve already explained, the locations of archaeological sites are not made available to the general public, due to the prevalence of looting. But there’s probably no harm in showing you the location of the old silo outside my dad’s former home (even though it could technically be considered a historical archaeological site, as it was built around the year 1900). It contains nothing of monetary value, and if you feel an urge to trespass there, be aware that the current landowners probably have a lot of guns, as is customary in rural Illinois.

Here is a satellite image of the old silo:

 

Figure 2. View of historical silo from space

Land surveyors in the United States write legal descriptions using a system known as PLSS (Public Land Survey System). I’ve noticed that even experienced archaeologists have trouble understanding this system, so I wanted to devote some special attention to it. The best way to explain PLSS is to start with the biggest units of land, and work our way down to the smaller divisions.

The silo outside my old home is located in Peoria County, Illinois, as shown below:

 

Figure 3. Map of historical silo's location imposed over Illinois counties

The state of Illinois is further divided by township. Essentially, it is divided into a set of perfect township squares, with each square covering 36 square miles (6 miles by 6 miles on each side). Each one of these squares is assigned two numbers—one for “township” and one for “range” (but the individual squares are generally just called townships). The "township" number indicates how far north or south the square is, and the "range" number indicates how far east or west it is. The township number is counted from an imaginary line called a baseline, which runs from east to west (for example, if the township unit is labeled as 9 N, that means its northern boundary is 54 miles north of the baseline). The range number is counted from an imaginary line called a principal meridian (for example, if the unit is labeled as 5 E, that means its eastern boundary is 30 miles east of the principal meridian).

That is how the term “township” is used in PLSS. It has a slightly different meaning in local politics. A “township” can also refer to an administrative division of a county, with its own small local government (road commissioner, accountant, etc.). These political units usually correspond perfectly with the 36-square-mile township squares I’ve discussed above. In some cases, the political boundaries of a township may be re-drawn to make governance easier, but the PLSS units are not supposed to change.

For example, I grew up in a remote area of Elmwood Township in Peoria County, Illinois. “Elmwood Township” is a political/administrative unit. It also happens to correspond with a 36-square-mile PLSS township unit located 48 miles north of the baseline and 24 miles east of the fourth principal meridian. Thus, the legal description so far would read as follows:

Township: 9 N

Range: 5 E

Principal meridian: 4th

Figure 4. Map showing silo's location and PLSS township boundaries in relation to baseline and principal meridian. The silo is located in the 9th township north of the baseline (hence, Township: 9 N) and the 5th township east of the principal meridian (hence, Range: 5 E). Note that the townships east of the Illinois River are counted from a different principal meridian, not shown in this map.

 

Figure 5. Map of silo's location imposed over PLSS township boundaries within Peoria County, IL. PLSS townships fit within county boundaries, but the county is not really part of the legal description.

Now, let’s work our way down to even smaller PLSS units. Each township/range square is further subdivided into 36 sections, with each section equaling one square mile. Section 1 is in the northeast corner, and the individual sections are numbered in alternating rows, ending at Section 36 in the southeast corner.

 

Figure 6. Map of silo's location imposed over section boundaries within Township 9 N Range 5 E

For example, I grew up in Section 23, meaning that the legal description so far is:

Section: 23

Township: 9 N

Range: 5 E

Principal meridian: 4th

Figure 7. Map of silo's location imposed over Section 23

In order to write an archaeological site’s legal description with the level of precision required by a state government, you generally need to divide the section into quarter sections three times. You will be narrowing down the site’s location to a square patch of land covering only 1/64 of a square mile. That is how precise your legal description needs to be.

First, I need to divide Section 23 into quarter sections: NW, NE, SW, and SE. The silo is located in the NE quarter. Then I divide the NE quarter into four quarters. The silo is in the SE quarter of the NE quarter. Finally, I divide that quarter into four more quarters. The silo is located in the SE quarter of the SE quarter of the NE quarter of Section 23. Thus, the full legal description reads as follows:

Quarter sections: SE SE NE****

Section: 23

Township: 9 N

Range: 5 E

Principal meridian: 4th

In all likelihood, you will need to do this for every site you record during a survey, and write the full legal description on the site form (Site forms generally do not require that you list the principal meridian, but you will have to name the county, and that should narrow down the location sufficiently).

UTM Coordinates

You will also need to learn a little about the UTM (Universal Transverse Mercator) grid system. This is a navigational coordinate system. When you use your GPS equipment to record the real world coordinates of artifacts in the field, you will often need to use UTM coordinates (as opposed to Latitude/Longitude coordinates, which belong to a different coordinate system).*****

Under the UTM grid system, the earth is divided into longitudinal zones. For example, the silo outside my old house is located in UTM Zone 16 North, which would be written as 16T. The precise UTM coordinates of the silo would be written as follows:

16T 255983 4514944

The first number (16T) indicates the UTM zone.

The second number (255983) indicates Easting.

The third number (4514944) indicates Northing.

It will be pertinent to know that the UTM grid system changed in 1983. The original system is known as NAD 1927 (North American Datum 1927). For some complicated geodetic reasons that I don’t fully understand myself, the 1927 system proved inadequate when being used with GPS technology, so the datum (frame of reference) was shifted, and the whole grid shifted with it. The new system is known as NAD 1983 (North American Datum 1983), and it was implemented due to the increasing usage of GPS technology at the time.

Why does this matter for archaeologists? Because the UTM coordinates written on old site forms often still use the 1927 system. In fact, archaeologists were still using the 1927 system until well after 2000. Old copies of USGS topographic maps use the 1927 system as well.

If I use the NAD 1927 grid system to determine the UTM coordinates of the old silo, I get the following coordinates:

16T 255976 4514736

Keep in mind that the silo itself has not actually moved. But there are two UTM grid systems, and they will give two completely different sets of coordinates to the same geographic location.

This issue is more likely to come up than you might think. There may be previously recorded sites within your survey area, and you will need to re-visit them during the course of your survey, possibly with the aid of the original site forms. But the UTM coordinates written on the site form may belong to the NAD 1927 system, and if you try to navigate to those same coordinates using the current NAD 1983 system, the coordinates will lead you to a completely different spot (about 200 meters south of the actual location). If you are reading or writing UTM coordinates, always be sure you know whether they belong to NAD 1927 or NAD 1983.

Unfortunately, many archaeologists during the old days were really bad at recording UTM coordinates, so the UTMs written on old site forms are often completely wrong, no matter which grid was being used. If you want to use a site form to locate a previously recorded site, but the UTMs on the site form are wrong, the best solution is to look for the physical features of the landscape that are drawn on the sketch map, which should be attached to the site form.

Quadrangles

Site forms generally require that you specify which "quadrangle" the site falls within. Personally, I don't think this is particularly useful information; this is mainly a holdover from the days when archaeologists plotted sites by hand on USGS topographic maps.

Quadrangles have nothing to do with PLSS units, and this can confuse archaeologists, so I'm going to break down what a quadrangle is.

A long time ago, the U.S. Geological Survey began producing topographic maps for the entirety of the United States. They created sets of maps at different scales, but archaeologists (and most other people) took to using maps made at the 1:24,000 scale (meaning that a unit on the map is 1/24,000 the size of its corresponding unit in real life). The USGS maps made at the 1:24,000 scale are known as 7.5 minute maps, because they cover a rectangular area corresponding to 7.5 minutes (a minute is 1/60 of a degree, and the globe is divided into 360 degrees). The rectangular area covered by a single 7.5 minute map is known as a 7.5 minute quadrangle.****** In effect, the USGS divided the whole United States into about 57,000 quadrangles, and named each one of them (they also created quadrangles at different sizes for maps made at different scales, but I'm not going to get into that, because archaeologists don't really use maps at the other scales).

These USGS quadrangles are perfect rectangles that cross state and county lines; they have nothing to do with the boundaries used by land surveyors or government administrators. However, the topographic maps themselves typically show PLSS units and UTM grid lines (be aware that maps made before 1983 will use the old UTM grid from 1927).

The historic silo I've been discussing falls within a 7.5 minute quadrangle known as Farmington East Quadrangle (named after the nearby town of Farmington, Illinois). The map below shows its location, imposed over the dozens of quadrangles that cover parts of the state of Illinois (note: this map does not show all quadrangles in the United States).

Figure 8. Location of historic silo imposed over 7.5 minute USGS quadrangle boundaries. The USGS has created a 1:24,000 scale topographic map for each of the rectangular units shown in the above map. The silo is located at the northern end of Farmington East Quadrangle.

Overview

This is the bare minimum of mapping knowledge necessary for conducting surveys and recording your findings. In fact, it’s less than the bare minimum, because I didn’t teach you how to use the various types of hardware or software. Ideally, if you want to make maps, you should also know a little about the principles of cartography, such as normalizing data, and knowing which map projections are appropriate for presenting which kinds of data. But I don’t have time for that here.

GIS and cartography have purely academic applications as well, both within and outside archaeology. I’m not going to discuss that here, but for those who are interested, there are plenty of studies about landscape archaeology and settlement patterns.

Footnotes:

*"Georeferencing" is the process of assigning geospatial coordinates to specific points in a pixelated image, such as a scan of a paper map.

**The term "GPS" refers specifically to the satellite system put into orbit by the United States military. Other countries have launched navigational satellites as well. The systems that include these satellites are known collectively as GNSS (Global Navigation Satellite System). Many of the devices that we colloquially call "GPS receivers" (and which I refer to as GPS receivers in this post) can also serve as GNSS receivers, if they are allowed to access international satellite signals.

***Not all states use PLSS, but if you are working in states that do, reading a PLSS legal description is an essential skill for archaeologists. Some states that used to be part of Mexico (such as Texas) do not use PLSS (for example, Nevada and California both use PLSS, and thus their site forms require legal descriptions, but Texas does not use PLSS, and thus does not include legal descriptions in its site forms).

****When I determined the quarter sections for this silo, I used the section boundaries on a USGS topographic map, not the Tigerline shapefile shown in the map I produced for this blog. The Tigerline shapefiles do not match up perfectly with the section boundaries drawn on USGS topo maps, but the topo maps are probably more accurate.

*****The numbers in a set of UTM coordinates represent meters on the earth's surface. For example, "northing" indicates the number of meters north of the equator. "Easting" is more complicated, which is why you also need to include the UTM zone in a set of coordinates. The Latitude/Longitude coordinate system is completely different—it divides the round globe into degrees, minutes, and seconds (in the same way that you can divide a circle into 360 degrees in a geometry class).

******The actual area that a 7.5 minute quadrangle map covers will vary by latitude. USGS topo maps use a conformal projection, meaning they preserve angular integrity (you can use these maps to follow a compass bearing), but in doing so, they must sacrifice areal accuracy (they do not show units as being the correct area, and this discrepancy becomes more pronounced at those latitudes closer to the poles). This is one of the complexities of trying to represent a round planet as a flat surface.

Other Resources

The sources below may be useful for students wanting to learn more about the academic applications of mapping in archaeology.

Barrett, J.C. and I. Ko. 2009 A phenomenology of landscape: a crisis in British landscape archaeology? Journal of Social Archaeology 9:275-294.

Hally, David J. 1993 The Territorial Size of Mississippian Chiefdoms. Archaeological Report 25:143-168.

White, Devin A. and Sarah L. Surface-Evans. 2012 Least Cost Analysis of Social Landscapes: Archaeological Case Studies. University of Utah Press, Salt Lake City.