Occasionally, I like to go through the QGIS plugins and see what’s new. There are all sorts of handy tools in there, but one in particular caught my eye this time. The Historical Map plugin, by Nicolas Karasiak & Antoine Lomellini, takes on a specific challenge: extracting data from old maps. Of course, you can always digitize this data, but it can be quite time consuming. The plugin leverages image classification techniques to speed up the process. The nice thing about historical maps (such as USGS topos) is that there are usually fairly discrete color codings. Discrete colors takes a lot of the guesswork out of the image classification process, but the techniques can be pretty intimidating if you haven’t done them before.
A popular cartographic element is the venerable hillshade. With a good hillshade and a transparent overlay, you can add a lot of topographic context to your map without being overly distracting. Most of us have probably used a bare earth hillshade before. These are great if you just want to look at the underlying terrain, or if you are covering a wide area.
For close-in work, creating a hillshade from DEM that includes the vegetation canopy can make things much more interesting. However, if you look closely at the canopy hillshade, you’ll notice that many of the terrain features no longer stand out, even where there is little to no vegetation. This is because individual trees and shrubs create more steep areas, which proceed to hog the dark end of the stretched histogram. So what’s a cartographer to do? Continue reading “Taking the Best of Both Worlds for a Better Hillshade”