Mapping

Been awhile since I wrote about maps.

I recently had a request to map the rivers in the Puerto Rican municipio of Ponce. I had already made a map of the barrios of Ponce for the same guy so I had my base map - I just needed to add the rivers themselves. I have several sources of digitized rivers but ran into a problem. A municipio is not a very large area, none of my river layers were detailed enough to capture the ones I wanted to show.

So I turned to the font of all geographic information - the USGS topo map. Topo maps remain the most detailed maps available for most of the U.S. and thanks to the wonder of the internet you can download scanned versions of them. Using GIS I can overlay the topo map on my base map and then literally trace the river lines.

So I finished and uploaded my map and then the downfall of using topo maps. Most of them are quite old. You don't think of rivers changing much, but they do. The requester pointed out where one of the rivers was re-routed from draining into the ocean to drain into an adjacent watershed by the army corp of engineers some 30 years ago. The new path is shown clearly on Google maps. With a little fudging I fix the map, check out the result at wikipedia .

Posted via LiveJournal app for Android.