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Victor Keegan, guardian.co.uk, Thursday 4 February 2010 11.34 GMT

If you want to find an up-to-date map of Haiti, then there is only one place to go. It is not Google Maps or any of its competitors. It is the admirable OpenStreetMap.org (OSM), which is being updated even as I write by volunteers all over the world.

It is the Wikipedia of the mapping world, and is used by millions of people. Started a little over five years ago in London by Steve Coast, it has steadily built up its database to the point where most of the world has now been mapped by a formidable team of volunteers which is doubling every six months: there were 212,000 at the last count, of whom 10% are active during any one month. At the end of January there were 239 people rebuilding the map of Haiti. For a bird's eye view of operations, go to the Ushahidi site.

When the earthquake happened it was a signal for OSM members around the globe to start downloading satellite images (either freely available or donated by Yahoo) and then to start tracing the outlines of streets on top so a map emerged. Volunteers on the ground in Haiti, often using Garmin GPS locators, added vital local information – such as which roads were passable, where the hospitals were situated, where refugee camps were, or walls, pharmacies, hedges and so forth – so rescue workers had an invaluable tool. The result is a new, detailed map that is updated frequently, unlike most commercial maps.

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