GIS for Archaeology, Module 9

For this week's lab, focusing on remote sensing, we worked with an aerial photograph of the area around Cahokia. Cahokia is a large Mississippian site in what is now southern Illinois. Constructed and occupied from about the 800s to about 1300, the city originally covered about 6 square miles and contained some 120 earthen mounds. Part of this area, including about 80 mounds, are now preserved as a National Historic Landmark and state historic site. It is the largest pre-Columbian archaeological site north of Mexico.

For the lab assignment, we obtained an aerial photo from the USGS database and performed two different land cover classifications in ArcMap, one unsupervised (classified entirely by the program's algorithms) and one supervised (classified with the guidance of a set of points with user-assigned values). The resulting maps are below. The unsupervised classification resulted in only three easily defined land cover classes, while I was able to create five using the supervised method and produce a more detailed image, but both contain many errors resulting from the algorithm being unable to tell the difference between similar pixels representing different land cover types (e.g. water and dark-colored trees, or pavement vs. a barren agricultural field). However, it might be possible to refine the supervised classification by adding additional control points. 

GIS for Archaeology, Module 8

This week the topic was 3D modeling, which I was excited about as there are numerous ways to use 3D modeling in archaeology. For this assignment, we used data from a shovel test survey to predict and model the stratigraphy across the entire study area, using ArcMap for analysis and ArcScene for visualization. I did my best to describe the size and orientation of these views, since ArcMap can't create an accurate scale bar or north arrow for a 3D scene. I forgot to note, however, that the shovel tests were dug to a depth of one meter, and these surfaces represent the top of each stratum.

We also used ArcScene to create a 3D visualization of the stratigraphy within the shovel tests themselves, and ArcScene's Fly tool to explore it. My video is a little awkward because I'm still getting the hang of using the Fly tool, but here it is:

Finally, we used the interpolated stratigraphic surfaces to predict the stratigraphy of a cross section of the site, using points along a line through the study area. Below you can see these points, with predicted stratum depths, fitted into the interpolations from before.

GIS for Archaeology, Module 7

This week was all about interpolations, and I ran many of them, comparing the results of different interpolation methods and different parameters for some of them. We used two different datasets for this lab, one for shovel test results from a site in Panama and one for population estimates for a regional survey in Ecuador. For the latter, we then used the interpolations to consider settlement patterning for a particular time period, having read an interesting article that described several case studies using a similar methodology. There are more complete descriptions on the map posters below.

GIS for Archaeology, Module 6

Over the last two weeks, we were tasked with a large multi-step project using data from the archaeological survey of the Valley of Oaxaca, which is not available in digital form. First, we needed to georeference a topo map showing the survey grid in order to tie the data to the correct locations in GIS. Each student was assigned two or three grid squares to digitize. Here is my section of the survey grid, digitized and overlaid on a topographic base map. 

For me this was the most challenging part of the lab--I was not able to get the survey grid georeferenced as well as I would have liked, which unfortunately means that the rest of my digitized data is also less accurate than it could be since it's based on those early errors.

The next task was to georeference and digitize maps of the land cover types and survey collection sites for each individual grid square. The sites are assigned numbers for each time period represented by the artifacts collected. My maps are a bit simplistic, but they do what they need to do.

Finally, graduate students had an extra task, to join a data table containing more information about the various sites to the collection sites shapefile. One type of data included in the table is population estimates for each site, so the final map shows one of my grid squares with sites classified by population size. (Note that this only represents one of the time periods included in the survey.)

Population size does not seem to necessarily correlate well with productivity of the land at/around the site, as most of my study area is characterized by relatively unproductive areas and it still contains at least one high-population site. And although many of the others are small, there are still quite a few of them.

GIS for Archaeology, Module 5

This week was all about georeferencing, specifically of historic maps, and the lab assignment was to georectify an image of Captain Cook's 1785 map of Macau and its surroundings. I found this really challenging because the area has changed so dramatically due to development that it was hard to see how the historic map should fit onto the modern one. It was also tough to find useful control points--the historic map just doesn't give us much to work with if we can't tell where the historic landforms are on the modern landscape.

Anyway, here's what I came up with (after more or less giving up after a certain point):

GIS for Archaeology: Module 4

This week's topic was historical imagery/maps, which can be incorporated into GIS and used to study a particular moment in the past or to look at changes over time. This can be particularly helpful with regard to changing landscapes or human activities that could impact archaeological sites. Historical data can also be used to identify potential archaeological sites that aren't yet recorded, including those which may have already been destroyed in some way.

Below is my lab assignment for the week, a poster about Paul Revere that includes a historic map. It also includes an image of a census record; historical census data is also a useful resource that can easily be incorporated into GIS.

GIS for Archaeology: Module 3

This week's lab assignment utilized data from the Middle Eastern Geodatabase for Antiquities (MEGA), an online database of archaeological sites in Jordan that includes site information such as location and condition (for monitoring purposes as well as research). It was developed as a way to help keep track of sites threatened by looting or other forms of destruction, and different users have varying levels of access to the data depending on their position and needs, although site locations are visible even to the general public, which is often not the case with databases like this. Below is a map created in ArcMap illustrating a selection of the sites for which data is available through MEGA.

The reason site locations are often not publicized, particularly in areas where looting and vandalism are common or in remote areas where it is difficult to monitor the condition of sites, is, of course, the need to protect those sites for the future. The safeguarding of archaeological resources, and the maintenance and preservation of records created and artifacts recovered through excavation, is a key principle of archaeological ethics. While there is sometimes a balancing act between the need to protect archaeological sites and the need to share data with fellow researchers and engage with the general public about the importance of archaeology, archaeologists must always keep in mind our responsibility to the archaeological record. Once a site damaged or destroyed, valuable information is lost forever. Thus ethical conduct by archaeologists is of the utmost importance--as is reaching out to educate the public (even if we sometimes have to withhold site locations in the process) so that people understand the significance of archaeological sites.