Cartography is a once-exotic specialty that is about to hit the mainstream. Making maps used to be supremely daunting. It required ultra-precise instruments and advance technical knowledge. A map could take thousands upon thousands of man-hours to build. And few might ever see it.

Three technologies are overturning this profession: GPS, digital imaging, and the web. An inexpensive GPS device allows almost anyone to generate cartographic data. Plotting software allows almost anyone to map that data out. And web technology allows almost anyone to distribute and view these maps.

Most of this recent amateur digital cartography is taking place upon the solid foundations of government-funded topographic mapmaking. The story begins by digitizing the current set of government topo maps. A number of agencies, including the National Geographic Society have completed this heroic task. They employed huge scanners which devoured entire maps at once, and software that stitched all the maps together seamlessly into one huge digital map. Once you have a digital topo map, you can port that stream of bits into a GPS device. Now as you hike or bicycle or drive with your GPS on, your path is traced onto the topo map automatically, or you can pinpoint particular spots. Back at your PC you can annotate your data.

For instance, let's say you are trailblazing a new path in second-growth forest in Vermont. Your trail can become a new layer on the standard topo for that area. You can indicate "spring here" or "cave there" or "bridge missing" and so on right on the map. You could survey the spreading meadow on a lakebed; this would appear on your digital map.

You can now share that map by posting it on the web. Someone else can download it, and continue to add their own data - maybe they mapped all the ruined remains of former farmhouses in the area. Over time the map begins to accumulate many layers of new and additional information. It might start off as the bare topo with contours and end up with amazing loads of data. Each layer easily repressed so you can select your view.

That first step - the digitization of the foundational topographic maps of the entire US - has just been completed by the United States Geological Survey. All 50 states are now available in digital form. The USGS licenses this full-country data to various companies. In parallel, National Geographic has recently re-scanned all 50 states topo maps themselves, claiming higher accuracy, higher resolution, and better interface tools. So now there are two basic pools of digital map services. Those depending on the USGS files are less expensive, more fragmented, and more like open source. On the flip side, National Geographic's data is easier to use, more expensive, more integrated, and less opened.