[OSM-dev] Extracting national boundaries
gary at gary68.de
Mon Aug 30 14:57:57 BST 2010
please have a look at boundaries.pl in the wiki.
hope this helps.
On Mon, 2010-08-30 at 11:05 +0200, Colin Smale wrote:
> I am trying to extract national boundaries from OSM and it's proving
> more difficult than I anticipated.
> What I would like to end up with, is a collection of complex polygons
> (inner and outer rings including enclaves/exclaves), one for each
> country. I thought I should be able to do that by getting all relations
> with type=boundary, admin_level=2. Using XAPI I got a large file which
> contains some of the information, but as some national boundaries seem
> to be implemented using subrelations and subsubrelations etc I now find
> I will have to query the database for each subrelation individually and
> drill down successively until I have all the ways I need. But that looks
> as if it will give me large numbers of internal borders between
> lower-level admin units as well, and it will be an enormous job to
> stitch everything together and discard the internal borders.
> For many countries there is a simple relation for the national boundary,
> referencing a number of ways, which I can concatenate to produce the
> complete outer boundary. But France and Slovakia for example don't seem
> to have a single relation as a starting point.
> I can't imagine I am the first person to want to do this. Has anyone got
> any tips? Or maybe even a ready-made data set?
> National boundaries don't change all that often, but it does happen from
> time to time, so it would be nice if this could be repeatable in the future.
> Thanks in advance for any help you can give!
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> dev at openstreetmap.org
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