[Talk-GB] Western Isles / Na h-Eileanan Siar

SK53 sk53.osm at gmail.com
Thu Mar 17 12:56:41 UTC 2016

A couple of days I noticed an issue with coastline ways tagged with
admin_level=6 which were causing many islands in the Outer Hebrides to
appear as county level admin areas. Co-incidentally someone reported the
same errors on the forum.

I hope I have now removed all boundary=administrative and admin_level=6
from ways which are part of the Western Isles district. There are still
many other coastline ways along the west coast of Scotland which need
similar treatment.

However in looking at the Outer Hebrides it became apparent that much of
the data is rather poor. There are four different factors:

   - Many of the coastlines are uncorrected PGS data often with systematic
   errors of placement of 100s of metres.
   - In some cases shadows on high cliffs have led to erroneous coastlines
   (notably Soay which should now be corrected).
   - The Western Isles boundary largely does not follow the coastline. It
   appears to mainly result from import of Boundary Line Open Data and
   therefore uses the low water mark. This data is generally more accurate
   than coastline data so many islands fall outwith or across the admin
   - Many islands are not actually part of the boundary relation at all.

Unfortunately these issues are rather intimately interwoven and coastlines
& boundaries are likely to get broken during the process of improving the

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