Testing Map Warper Beta

One of my biggest fears is the loss of data because of improper preservation, irrelevance to the public and hoarding.  As a geoscientist, I love maps, especially old ones that tell long stories of where people lived, how their land use priorities changed through time and how sprawl develops.  I also believe in more than one instance of a map.

Tim Waters has developed an open source tool called Map Warper (Beta) into which you can upload a scanned map, georectify it and save it out as an image or a map layer.  As a former resident of New Orleans, where a transparent recovery and historic preservation are daily uphill battles, this tool can be invaluable in saving and sharing ancient and new maps of the city’s original development and re-development since Hurricane Katrina and The Flood.  The following shows how, in under ten minutes, I georectified an 1895 map of the French Quarter and Garden District of New Orleans and exported it to Google Maps.

Map Warper works by rubber-sheeting: Side by side are the old map and a “new” one with a known coordinate system.  Mark a known location on both maps, generate three or more of these control points and the application stretches/warps the old map like a rubber sheet onto the new one.

Georeferencing old map with new one by generating control points

While Map Warper suggests at least three control points, I advise generating control points at edges, map centers and in the specific area of interest within the map. This greatly helps an accurate warp.  Use known landmarks and street intersections as much as possible.  It also helps to know the city with which you’re working, so work on your own city or get the assistance of someone who knows the lay of the land.

Click on Preview Rectified and here’s the result at 70% transparency:

If you look at the map closely, you will notice that the match isn’t exact.  This is why I suggested control points at the edges and in areas of interest.  The important point, however, is that Map Warper has no learning curve associated with it and only requires your knowledge, time and patience for increased accuracy.

Once done, you have the option to download the warped layer as a .kml for Google Earth, send the layer directly to Google Maps to create your own private or public map or export images.  Remember that the program is still in beta, so expect some bugs.  Try it out and write in with your results!