OS Openspace API
When Ordnance Survey finally released the API for their digital maps last year the new possibilities available to developers seemed endless. Despite the fact that 1:25000 maps aren’t available (come on OS!) there are now a few sites out there that are making good use of the data.
If you just want to see what Openspace has to offer click here, where you can see a basic large ‘slippy’ map.
If you save your walking routes from your GPS, this page is great. It allows you to overlay your routes as .gpx files onto 1:50000 os maps. I hope to integrate this into my site at some point in the future when I get the time.