OpenStreetMap is a collaborative project, much like Wikipedia but for road maps. The map available on the site is searchable by keyword, postal/zip code etc. like other online map services, but the content is completely royalty free, available under a creative commons license. The map is generated by users of the site with commercial GPS units.
I had heard of the project in the past, but it wasn't until I was doing some research into GPS modules for a university project that I discovered how cheap these units had become. I bought a handheld Garmin eTrex unit from Amazon for around £65, but USB devices are available for as little as $25 in the US. Once I had a GPS I wanted to put it to use, and not being particularly fond of walking for the sake of it I looked into doing some mapping for OpenStreetMap (OSM).
Initially I was disappointed that the coverage of Bath was excellent. This is great for using it to find places in the city, and it has a really nice print-out format for taking sections of the map with you, however it left me with nothing to map. However, Guernsey was completely blank with only the airport marked, even the coastline wasn't right. This left me with a challenge for my 3 week Easter break, how much of the island could I map?
You can currently see how much I got done on the main map at OSM. I managed to get a fair few roads in (despite an absurd number of those roads being closed at some point in the three weeks.) There are quite a lot of extra roads that I logged with the GPS, but to display on the map a line of best fit needs to be drawn by hand through the GPS points and labelled with the road name.
It was quite a challenge to get that much of the island mapped over the short time I was at home. I logged some of the obvious routes quickly, the trip to work, trips to see grand parents etc. I only made a few special mapping trips and I mainly combined these with photography expeditions. My parents were a great help in the mapping project taking de-tours from the usual routes (sometimes quite large ones) to get an extra couple of roads, and their help with naming all the roads was invaluable.
If you're from Guernsey and want to have a go at filling in some of the gaps, please do, it's pretty easy to do once you've got the Java client (creatively called Java OpenStreetMap) installed. The main thing you need to know is what the road names are and where they start and end, and for copyright reasons you can't use another map to find out these things.