The United States Geological Survey’s National Map makes use of a corps of volunteers, who are assigned a given area (a USGS quad) and report the names and coordinates of various map features, such as schools, town halls and other facilities, and any changes thereto. The sorts of things that aerial surveys might reveal, but not necessarily identify. Sounds interesting — something a dedicated individual with spare time and a GPS might have a lot of fun doing, akin to what OpenStreetMap volunteers are doing in the UK. (U.S. geographic data is in the public domain, so this may well be the next best thing.) Via Very Spatial and Catholicgauze.