Geographic Information Systems (GIS) allows us to display multiple layers of information and data on one map. This makes it possible to generate maps that provide new ways of examining historical topics such as slavery at South Carolina College. One tool of GIS is georectification, a process of overlaying maps. The spatial features of the campus in 2010 are overlaid on a Sanborn map of 1884. By linking the maps with control points we put the historic map on a modern coordinate system. The software reshapes the old map to resemble the new one.
We begin with two maps: an 1884 Sanborn map and a “shapefile” of the buildings on the current campus:
This 1884 Sanborn Map shows the “footprints” of outbuildings on the nineteenth-century campus. The Sanborn Fire Insurance Company created these maps to underwrite insurance policies throughout the United States; they now serve as a valuable resource for urban historians.
This shapefile appears less detailed than the Sanborn, but the shapes are on a coordinate system. This accuracy enables GIS to link points on the old map to coordinates on the new map.
Six control points are used to georectify the 1884 Sanborn Map. The modern buildings appear as black polygons around the older buildings. This map allows us to see where outbuildings stood relative to current buildings. From this map, we see five two-story kitchens / slave quarters behind professors’ houses. Most of the outbuildings have been demolished, but one still stands behind the current Presidents House.
Of course, you can add more than one layer:
This map adds the current parking lots, gardens, and sidewalks to the last map. The transparency has been increased to fifty percent in order to show the nineteenth-century features that are no longer visible. It is more difficult to see the footprints of outbuildings in this map, but that is the point. The interior of today’s Horseshoe is an antebellum landscape, but modern features hide the outbuildings. GIS enables us to imagine this forgotten layer of history.