OpenStreetMap: Cracking open cartography

Britain has a long history of map making. Ordnance Survey was set up in 1791 to create accurate maps of southern England in preparation for a French invasion. The information in these first maps was seen as vital to protecting Britain's interests. Now, over 200 years later, Ordnance Survey protects its extensive mapping data just as closely. It turns out they're not the only ones — most sources of geographic data and maps are proprietary, which can make including them on websites and in applications expensive and restrictive. The latest web-based collaborative project to hit the headlines aims to change this.

The OpenStreetMap project was started by programmer Steve Coast nearly three years ago as a way of overcoming the difficulties involved in using geographic data with open-source software. Today, the project is still in its infancy but is growing rapidly, and is probably the most active open-geographic-data project on the internet.

Its aim is simple: map the planet. Contributors to the project use GPS receivers to record the location of geographic features and eventually build a database of every physical feature on Earth, making it available under a free licence. While that goal may still be a long way off, it's clear that people are interested in creating the data and tools needed to achieve it. More than 3,000 contributors are submitting map data, and dozens of people are writing programs to gather, edit and display OpenStreetMap's information.

Coast's initial reasons for starting the project were more practical than idealistic. "I had bought a cheap USB GPS for my laptop and wanted to use it with some open-source software on Linux. The software all existed but the data didn't, so you had to download and save maps from Microsoft MapPoint — as it was then — which breaks copyright and the terms and conditions. If you wanted to drive somewhere, you would have to open the software and pretend to drive [the route] while downloading the map images. They could then be replayed to you as you actually did the route. You couldn't use the images for routing and, if you diverged off the images, then you had no map," he explains.

Coast found that there were no maps or geographic data available that could be used with open-source software, and, if he wanted some, he'd have to create them himself. "It seemed pretty silly. So I figured I could make a map using a GPS and then, if I could, then so could you. Then we could join our maps together into one big map and, with enough people, maybe all of London, or the world. It seemed like a fun thing to attempt to get it all working."

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The philosophy of OpenStreetMap is identical to the web's biggest free-content project, Wikipedia: many contributors each add a small part to the whole, and successive contributions both expand and improve the information. Unlike Wikipedia, participation often requires more than just typing. "The difference is that Wikipedia doesn't care where you are if you can contribute to the article on cheese," says Coast. "OpenStreetMap needs you to go where you're mapping in order to collect the data — or have a very good memory. It's more active — if you want to contribute more than a small amount of data, you have to get out and about."

Data is gathered by contributors walking, driving, cycling or otherwise making their way along streets, paths or other features, with a GPS receiver recording their every move. The breadcrumb trails generated in this way are then used to trace the points and paths needed to create a map. The need to own a GPS receiver appears to have affected participation across different demographic groups so far — Surrey has far better coverage than Sunderland, for instance.

Despite OpenStreetMap being started in the UK, it's already attracted attention from other countries. Germany, the Netherlands, Spain and Sweden all have people providing data. Coast believes that people in other countries where data is difficult or expensive to obtain are also generating a lot of contributions. "It started in the UK, so here we have the most mappers. It's taking off in Spain, Germany, Denmark and the Netherlands without doubt. We're seeing huge growth in those places, and other countries here and there. Recently, the mappers in the Netherlands got funding to run mapping parties, which has meant a huge boost to the level of data there. Similar things are happening all over the place. It's happening a lot in countries with national mapping agencies which are monopolies, much like the OS [Ordnance Survey] in the UK."

All of OpenStreetMap's data is licensed under the Creative Commons Attribution-ShareAlike licence, which means that...