OpenStreetMap is an ebook by Jonathan Bennett that teaches you how to become your own cartographer. The book and its accompanying technology allow you to to create your own custom maps or ‘GPS Traces’.
A GPS trace or tracklog is simply a record of position over time. It shows where you traveled while you were recording the trace. This information is gathered using a GPS receiver that calculates your position and stores it every so many seconds, depending on how you have configured your receiver.
If you record a trace while you’re walking along a path, what you get is a trace that shows you where that path is in the world. Plot these points on a graph, and you have the start of a map. Walk along any adjoining paths and plot these on the same graph, and you have something you can use to navigate. If many people generate overlapping traces, eventually you have a fully mapped area. This is the general principle of crowdsourcing geographic data. You can see the result of many combined traces in the following image. This is the junction of the M4 and M25 motorways, to the west of London.
To collect traces suitable for use in OpenStreetMap, you’ll need some kind of GPS receiver that’s capable of recording a log of locations over time, known as a track log, trace, or breadcrumb trail. This could be a hand-held GPS receiver, a bicycle-mounted unit, a combination of a GPS receiver and a smartphone, or in some cases a vehicle satellite navigation system. To record additional information about any features you’re mapping it is advised that you have handy and notebook and pencil (for noting down street names etc), a voice recorder (for audio mapping) and digital camera (if you want to add visuals).
You can dramatically improve the accuracy of your traces by putting your GPS where it can get a good signal.
The above image shows a low-quality GPS trace. If you look at the raw trace on the left, you can see a few straight lines and differences in traces of the same area. The right-hand side shows the trace with the actual map data for the area, showing how they differ.
For anyone experimenting with mobile mapping techniques, OpenStreetMap is a user-friendly introduction to becoming your own cartographer.
For those wanting a more in depth take on the uses and abuses of mobile and wireless mapping technologies see Katherine S. Willis’ recent article ‘Mutable Territories‘ in the excellent Digital Art online journal Vague Terrain. Katherine produced a map of her own movements over using a similar technique to the one described above.