Historic Maps - Georeferencing

     This week we continued using historic maps but took it a step further. Instead of being provided with a previously georeferenced map we performed that task ourselves. The data for this assignment came from the David Rumsey Map Collection. Specifically, I used the Geographical Searching with MapRank Search to find an historic map of Macau. The map was authored by William Bligh (1754-1817) and James Cook (1728-1779) and published as part of a collection of maps detailing the explorations undertaken during Cook's voyages. The links provided presents more information about the publication and the men themselves. 

Georeferencing

After acquiring the map it was cropped to eliminate irrelevant portions of the image (like the pages and cover). The newly edited image was imported into ArcMap and georeferenced. The historic map shows a much different landscape than that we see for modern Macau. This made the search for control points a challenge. In addition, the historic map was inaccurate (things seemed to align fairly well vertically but were off horizontally). Some features, however, are still present on both maps, like Illa Verde. At any rate, once I had enough control points (n > 10) and a reasonable RMSE (considering time management on the lab), I used a spline transformation to acquire the georeferenced image you see below. The map deliverable shows the georeferenced historic map (40% transparency) over aerial satellite imagery for Macau, China. 

The map deliverable showing the georeferenced
historic map of Macau displayed atop aerial imagery.

    A quick note, if you have some spare time to peruse old maps then let me recommend the site I referenced earlier. The David Rumsey Map Collection is chalk full of neat ways to visualize historic maps. They have georeferenced historic maps displayed on Google Earth where you can compare historic and modern map images. Additionally, they have a 3D GIS Viewer in which historic maps are combined with DEM from the same area to make a 3D historic image. Tell me that doesn't pique your interest. Explore the rest of the site because I am only touching on a couple of the incredible things you can distract yourself with.