A few weeks ago, I got in touch with Robert Clynes from the Isle of Man Department for Local Government and the Environment, the Department with responsibility for GI on the Island. My request was simple: are you interested interested in helping out OpenStreetMap? The response was equally simple too – yes, they were. I little while later, Robert sent me this GeoTIFF of the Isle of Man, that OSM have been given permission to derive data from.
Kristian Thy form OSM, put the image onto a WMS server that he runs, and now the map is available as a WMS layer. From here, we can import the layer into JOSM, using Chippy’s WMS plugin, using this WMS URL:
http://quovadis.dk/cgi-bin/man.cgi?SERVICE=WMS&
VERSION=1.1.1&REQUEST=GetMap&layers=man&srs=EPSG:4326
&format=image/png
The results look like this:
The north of the Island being edited in JOSM
St Johns – in the centre of the Island
One of the first things I noticed was how nearly-complete the mapping of the Isle of Man is. Looking at OpenStreetMap data of the Island, I had estimated that about 60% of the roads were mapped. Validation is a major problem when collecting geo-data. How do you know that you know where something is? Who do you trust to tell you where it is? OSM has an additional problem that in that its completeness, in the UK at least, is measured against the benchmark of the Ordnance Survey. A public admission by an OSM contributor to using Ordnance Survey data to verify their mapping could open up a whole can of nasty worms and threaten the future of the project. Of course comparing OSM data to OS data would not necesserily breach any OS copyrights – but any attempt to do so would have to exercise a lot of caution. In this case however, we are able to both compare and trace from a map that is derived from a the Isle of Man’s master data set. Why is this so?
As a self governing nation, the Isle of Man is responsible for its own mapping. In the past this has largely been carried out by the Ordnance Survery who are contracted by the Manx Government, who retain copyright of the map data produced. See here for more details. The licensing is pretty reasonable, and most importantly the details are contained in a few PDFs on one webpage. The standard license wouldn’t usually allow someone like OSM to apply its CC-by-SA license on derivatives of their data, but in this instance we have been given special permission to use the data. I’m going to try and get the entirity of the map traced by the end of the weekend – happily coinciding with the OSM Carto Day in Oxford, which should lead to some beatifully rendered Mapnik tiles of the Island.
