Grab your GPS, set it logging, wander about a bit, and visit openstreetmap.org

In a recent shoot-out between my little Garmin i3 and a mate's considerably more expensive expensive TomTom Go, the Garmin won, hands down. On the same route, leaving at the same time (in Dartmoor, Devon), the i3 got me to our destination 10 mins ( 1hr 30 min journey) quicker despite the fact that I stuck to speed limits and he admitted he didn't.

Anecdotal tales I've heard from others also suggest that the Garmin devices are less prone to off-roading you than TomTom.

hmm, wiki mapping. Potential for much abuse, especially by certain authorities.

Though I'm not sure of the point when Google et al have done all the work anyway with some seriously nice sat imagery too, and GPS logging can be tied in with the likes of Google Maps/Earth.

Tim, there are many possible points:

- Not having to pay TomTom/Garmin/whoever 100EUR each year for an updated map.

- Having the map updated more often than once each year.

- TomTom doesn't currently offer a map of Greece. OSM could (in the future).

- None of the major nav system vendors are likely to be offering maps of Congo or Laos any time soon (to pick two examples at random). OSM could.

- Providing free maps to Wikipedia, books, whatever.

- Non-car users - there are bunch of people at OSM concentrating on the UK's national cycle network, for example. So you'd have the prospect of one day having a specific routing device (or at least a specific map) for cyclists.

- Providing richer maps. Marking each post box, telephone box, whatever people are interested in finding.

There's not enough money in several of these points for TomTom or Garmin (or Navteq or whoever) to be that interested in satisfying them.

Most importantly, it's fun to do.