Poster Presentation C Thursday, 5:00 6:00 pm C Edmund Fitzgerald Exhibit Hall

Comparing Past and Present Landscapes

Tim Wallace, Carol Gersmehl
Macalester College
Department of Geography
1600 Grand Avenue
St. Paul, MN  55105

In our spring 2001 GIS class, we used geo-referencing tools to compare past and present landscapes. We will show two projects. One major project goal was to evaluate the route of a canal proposed to cross Maryland (Delmarva peninsula) in the early 1800s. The canal was delineated on a map from the first decade of the 1800s. Previous analysis of this historical map using GPS in relation to archaeological features showed the map to be remarkably accurate. Methodology involved several steps. First step included use of a 1:24,000 DRG and GPS points to geo-reference the historical map. A later step also used the 1:24,000 DRG as the basis for digitizing contour lines which could be converted to a TIN. Then the geo-referenced historical map could be draped over the TIN. The resulting image showed the location of the proposed canal in relation to the topography of that local area. A less complex project compared air photos of downtown St. Paul from 1940 with 1957 and 1997. The 1997 image was a DOQ from the Metropolitan Council, and the 1940 and 1957 air photos were scanned TIF files from the Borchert Map Library. ArcView's Image Analyst extension was extremely helpful for geo-referencing the old air photos, and The Lawrence Group street files were very helpful during the geo-referencing process. The change from 1940 to 1957 and then to 1997 is a useful stimulus for questions about historical urban change. These projects illustrate the use of geo-referencing historical images (maps, air photos) to facilitate understanding archaeology and historical geography.