On 1st April, Ordnance Survey released a lot of their data under an open data licence, allowing it to be used freely (with an attribution to say where it came from) and incorporated into other open data projects like OpenStreetMap.
The OpenStreetMap project started off in the UK because Ordnance Survey was so restrictive over the use of their data, so this has been a great win for the project, though the release of the data doesn't make the project any less likely to continue. This is partly because of the project's aim to create an open map (and open map data) for the whole world, and partly because in many parts of the UK, OpenStreetMap actually surpasses the level of detail that Ordnance Survey has released as part of their OpenData package.
Where the Ordnance Survey data comes in very useful for the OpenStreetMap project is in areas where we don't (yet) have much map data, as well as for areas where we do have a lot of data, for checking that our data is accurate and complete.
A little while ago I noticed that Canvey Island hadn't had much attention in OpenStreetMap, with just a few roads that had been added by a couple of users over the past two years or so. Curious about the place (and for some reason, partially imagining it to be a little like Coney Island in New York) I started to read a little about it, and thought about visiting, but the more I looked at it, the more I wanted to fill in the map. The result is below.
The OS OpenData allowed me to add roads (and most of their names), museums, libraries, pubs, schools, churches, camp sites, caravan sites, chalet villages and some natural features. Where things on the OS map didn't show names, it was often possible to pick these up from photos on the excellent Geograph project and from other research on the internet.
Once I'd got most of the tracing work done, I also got in touch with the two local contributors I had identified, one of which got back to me straight away (despite not editing the map since last year some time), and added in any extra information he could, such as the extent of parks and recreation grounds.
I think this is a great example of one open data project being advanced by the availability of data from other sources and projects.
If you want to help mapping an area (it's probably best to improve the map in areas that you know rather than mapping an area like this that you don't know that well...), just follow the instructions on the OpenStreetMap wiki.