Scottish Popular Edition Tracing for OSM

The provision of free-for-any-use spatial data for the UK may be changing dramatically on April 1 with the anticipated release of some Ordnance Survey mid/small-scale mapping and data for unrestricted use.

Until then, the only Ordnance Survey maps that have been able to be used to derive data from for the OpenStreetMap project in its bid to complete coverage in the UK, are those that are more than 50 years old and therefore not protected by Crown Copyright.

Scans of such maps, generally the New Popular Edition from the 1940s/50s, have been available for some time now – the scans were originally done for the NPEmap project (gathering copyright-free postcodes by asking people to geolocate them to the maps) and then were orthogonalised and reprojected from the British National Grid into the “Web Mercator” projection used by Google Maps, the “standard” OpenStreetMap website and numerous other online “slippy” maps.

Scotland wasn’t included at the time, partly because the maps were sourced differently. After consultation with the owners of the scans, I’ve taken the imagery, rectified, reprojected, stitched and tiled it using TimSC’s warp-gbos tools, so that it can now be used to trace Scottish data.

The source maps are at 1:63360 scale (one inch to a mile) and typically there remains an error of around 10m – up to 30m in some places, and of course more where the source map was drawn slightly incorrectly. So the imagery isn’t particularly useful for detailed mapping – particularly in cities which have seen significant growth in the last 50-80 years since the maps were made. However they are very useful for completing the rural road network, town and village names and natural features (hills, rivers) that are unlikely to have changed significantly recently – the low-res Landsat imagery can be used to show the presence of more recent forests or reservoirs.

In the above example, it would not be unreasonable to assume the path here still exists, and add it in – citing the source. You could also add the cliff, and reshape the lochs slightly from their current jagged Landsat-derived image. Adding in names for the hills and the lochs are also a definite benefit, although these old maps tend to have the Anglicised versions of names – newer editions of OS mapping for the Highlands of Scotland tend to use more authentic Scottish-Gaelic names. (Not an issue in this particular example, just north of Slioch in the Great Wilderness, as all the names on the map are in Gaelic.)

You can see the map tiles while editing OpenStreetMap data in Potlatch for Scotland, by selecting “UK Historic: Scotland” in the Potlatch preferences pane. They are available to zoom 15, although zooms 14/15 are simply smoothly interpolating pixels. The tiles are hosted on a computer under my desk here at UCL. There are better quality and higher resolution scans of more recent maps for some parts of Scotland, information about these is . The main advantage of the Scottish Popular Edition tiles over using just these they offer substantially complete coverage of Scotland.

(Strictly, some of the areas are using newer mapping which is still more than 50-years old, but is part of more recent editions than the Scottish Popular Edition).

So, the main benefit – having a map with full coverage of Scotland which can be traced from for OpenStreetMap – may be diminished, if a useable equivalent appears shortly which is only a few years out of date (i.e. Ordnance Survey Landranger/Explorer), but for now, they are still a useful source of base data.

If you just want to look at the mapping rather than editing them, you can see them here on my own site, or here on the NPEmap project.