Geo-referencing at Sapelo Island
Overview
After Chocolate Plantation was aligned to the proper location a second map was imported from Nicholas Honerkamp’s survey of Chocolate Plantation. This map included the outlines of the structures and the historic tree line as well as the actual tree line of the property. The information on this map was aligned to the satellite image through the alignment of the corners of the structures in a manual process. Points of commonality were assigned and the image was adjusted accordingly.
The final step was to begin creating the final footprint layer. This layer would consist of polygonal outlines which would be assigned information in a database. This was done through the editing toolbar. The polygons were drawn using the polygon and rectangle tools. Next, the database was created. This was done through the creation of an attribute table. This attribute table had a value and row assigned to each polygon which had been drawn, making the entry of data relatively easy. Categories were created for the date of construction, quality, building uses, date of scans, number of scans and data was entered for each category.
This project focused on the use of georeferencing in the program ARCMap as a way to create geographical databases. The goal was to create a map of the site at Chocolate Plantation and add a database which had values assigned to each one of the structures at the site. This database would present information such as date of construction, condition, date scanned, and number of scans. The purpose of doing this is to present information in an interactive and visual way, making it easier to reference the site when looking over data. This method of presenting information also tends to be more engaging that just presenting it traditionally in written form. Having this data attached to a map of the site also makes it easier to keep track of data and reference it to a geographical location for future use. The map created has multiple layers, and is georeferenced to Chocolate Plantation’s actual location on Sapelo Island, Georgia.
The Process
The first step in the project was acquiring a shape file of Georgia with visible county lines so that Sapelo could be accurately located. This was found online through the McIntosh County Government website which used the map for tax and auditing purposes. This shape file was imported into ARCMap as the base for the map. Having this base shape file map allowed for things to be georeferenced to their proper location within Georgia.
The next step was finding a satellite image of Chocolate Plantation. This was done through Google Maps by screenshotting the location. Four reference points were marked in Google Maps as well. The coordinates of these reference points were copied down so that they could be referenced in ARCMap. The screenshot was imported into the program and set on a separate layer above the map of Georgia. Afterwards, the process of georeferencing began. This was done by placing those same four reference points around the screenshot and entering in the coordinates. The program automatically lined up the two layers based on the coordinates to reflect the actual location of the plantation in Georgia.
County map of Georgia with the location of Chocolate Plantation circled in red
The data entry process through the attribute table
The geo-referencing process
References
1 Honerkamp, Nicholas and DeVan, Rachel L. (2008) "Pieces of Chocolate: Surveying Slave and Planter Life at Chocolate Plantation, Sapelo Island, Georgia," African Diaspora Archaeology Newsletter: Vol. 11 : Iss. 2 , Article 6.