René Descartes

The very first step in exploring a new archaeology site is setting up the grid. Remember the x,y coordinate system from elementary school? In high school the teachers called it the Cartesian coordinate plane. We superimpose one of these imaginary grids over the archaeology site so we can map all of our finds.

Rita sets up the transit.

We start by setting up the laser transit at our (0,0) location, or the datum. We use a grid north rather than true magnetic north. Our grid north is aligned with the town plan of Savannah. So as you drive towards the Savannah River on Bull Street, you are following our grid north. We use the transit to identify the location of more points along the grid, putting large nails into the ground to mark important points. The transit shoots a laser towards the prism rod, and the laser bounces off of the prism back to the transit. From this, the transit computer calculates distances and angles, allowing us to precisely identify any point with our grid.

Laura holds the prism rod while Rita operates the transit.

We map in all of our excavations, ground penetrating radar areas, and special finds. We also use the transit to map significant locations such as roads, buildings, monuments, and other obstructions. At the end of the day, we go back to the office and download these points (or coordinates). I can use basic drafting programs to make simple maps, or I can put these coordinates into our GIS (Geographic Information Systems) database and make more complex maps. (I’ll be posting more on GIS in the future.)

On last Tuesday, we began setting up our grid near the corner of Fahm and Zubley streets in Savannah. We established the grid, and Dan ran his ground penetrating radar (GPR) machine over the grassy greenspace between apartment buildings. We believe this area is the location of one of the redoubts (mini forts) that surrounded Savannah in 1779. Once the data is collected, Dan will use a computer program to post-process the data, producing 2-D and 3-D images of what anomalies lie beneath the surface. The GPR images will suggest what archaeological resources are present. However, the only way to know for sure is to dig, looking for artifacts and old soils. This process is called “ground-truthing”. I’ll let you know when we have GPR results!

We took advantage of the rain on Friday and visited Luciana at the Savannah City Archives. She helped us find many maps of the project area. Even though the Archives does not have any Revolutionary War maps, later maps are also helpful. We have to understand everything that has happened in between the Rev War and today in order to understand the archaeology site itself. For example, maps showing the Civil War fortifications can help us eliminate areas to dig. Or if many buildings have been built and rebuilt in an area, there might be many feet of other cultural layers covering up the Revolutionary War layers.
Thanks Luciana!
 

Rita examines maps in the Savannah City Archives.