Slough Creek update: Still distracted by the building footprint data. I figured the thing to do was open the data in QGIS and then add a polygon layer and clip out a smaller area. But, opening the data in QGIS for Kansas seems to run my PC out of memory or something. I can open a small file, like D.C. without much trouble. I was able to open Kansas and added a polygon. But as soon as I moved the mouse to the menu to clip the vector layer my PC froze.
I tried something else and this worked. I put the data in
mapshaper.org. The raw data is geojson. The
mapshaper.org page lets you export the data as a shapefile. That worked pretty well. I used Kevin Shipley's old copy of Global Mapper to clip out a bit of the shapefile and then can easily open it in Open Orienteering Mapper. Success!