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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