[Talk-GB] Relations

Bob Hawkins bobhawkins at waitrose.com
Mon Mar 1 15:38:53 GMT 2010

I have been following with interest the recent posts regarding the creation of administrative and electoral boundaries in OpenStreetMap.  OS 1:25000 out of copyright maps now available for my area plus other non-copyright information I have, allow me to contribute.  However, I do find relations confusing and there does not appear to be much written on the subject to help.  I use JOSM and should appreciate comments on the following:
New civil parish boundary, for example
1) Create a new relation.
2) Select all ways that form part of a given boundary, such as roads, paths and waterways, and add that selection to the new relation.
3) Any ways forming part of a boundary not already in the OSM database must be created, selected and added to the relation.
4) What happens if a boundary crosses open countryside not apparently following any feature, not even a wood edge or fence?  Must a way with a boundary key and value be created?  Then, surely, all existing ways forming part of a boundary must have boundary keys and values added?  Does it follow, then, that the first step is to actually add a boundary key and value to all existing ways forming the boundary?
5) I assume the boundary should not be created as a completely separate entity, but that it should make use of existing ways where they form part of the boundary.
6) How do hierarchies in administrative boundaries work?  I see a way in the River Thames tagged as a waterway and county boundary only with key=admin_level/value=6, key=left:county/value=Buckinghamshire, key=right:county/value=Berkshire;Oxfordshire).  Is this correct, or should this boundary information be in the relation only?  In other words, should all administrative boundary ways simply have key=boundary/value=administrative?
7) Is there any meaning to the order of the ways in a relation?  For example, the selected relation editor offers two buttons: "Add all primitives selected in the current dataset after the last member" and "Add all primitives selected in the current dataset before the first member".
8) What is a 'primitive'?
9) Is a boundary relation seen to be complete once the final way connects to the first way?
I am sure I could compile many more questions.  By no means do I demean the tremendous work done for OSM contributors - I am full of admiration, but I do wonder why, when so much preparatory work has gone into the construction of something, there is sometimes so little associated explanation or help.  I should so appreciate any further information on the use of relations, and with particular regard at the moment for administrative boundaries, which seem to be concentrating so many minds.
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