Thoughts on Geo-Referencing

Alice K Cutter
Sat, 22 Oct 2022 00:41:24 +0000
Week 6, Georectifying, Georeferencing

Using the David Rumsey map collection I tried to rectify or fix two maps. The process of rectifying maps involves matching points on a world map to points on your given map. The first map I tried to fix was a map of a 19th century French fort. The map showed a fort situated next to a bend in the river. What was difficult about rectifying this map was that I had little idea where it actually was. This is because the fort today no longer exists. The second map I rectified was a lot easier and was perhaps more interesting. It was a map of Mississippi and Louisiana from 1857. Because state boundaries are still quite the same today as they were in the 19th century, matching up the points was easy.

When I was finished matching up points I selected to see the overlay of one map onto the other. You can see the map overlay here: https://davidrumsey.georeferencer.com/maps/dc548093-07d6-502d-b577-4464fe80f465/ Initially, I thought there must have been a mistake. Louisiana protruded much farther out than the current day map. It was then when I realized that in 165 years sea levels had risen such that the shoreline looked completely different. I was shocked. I knew climate change caused rising sea levels but to see it jump out when I didn’t expect it was surprising and exciting.

This difference in coast lines sparked my interest. I think an interesting future project would be to use old maps to recreate shorelines. It would be fascinating to show what the view would have looked like looking out into the gulf of mexico in 1860 and compare it to now using georeferencing as part of the processes.

Before I go too far spouting the benefits of geo-referencing, I should say that it is not a fix-all solution to all old maps and problems. Some maps, like the french fort, do not translate well. Additionally, maps drawn in perspective (ones that show a view of sorts) do not translate well. This is because geo-referencing uses the Mercator projection which looks at the world from a birds eye view. Despite this, geo-referencing is still a really neat tool. What’s impressive about the David Rusmey site is that you can export the map in all sorts of different formats and file times. Some of these included: Web Map Tile Service (WMTS), TileJSON link and XYZ link. With all these formats the possibilities are endless of what can be achieved with geo-referencing.