[Tagging] Feature Proposal - RFC - Place areas

Joachim noreply at freedom-x.de
Sun Jun 18 16:59:52 UTC 2017


The mapping of settlements as place areas has long been hindered by
several problems:
* The usability of place=* polygons (huge closed ways, multipolygons)
* The centre information would be lost
* The extend of a settlement is not explicitly defined
(https://en.wikipedia.org/wiki/Settlement_geography). This might lead
to disputes

For the first two points I present a solution. For the third I thrust
national/local mappers to converge.

I present two new tags and three scenarios of which the first one
holds the most promise:

For settlements (or parts of) which have a centre the tag
boundary=place is introduced to be used on
- closed ways (areas)
- also on type=boundary relations.
... as already done by administrative boundaries, postal codes and low
emissions zones.

The place node is kept and put in the relation as role place_centre.

Places without a centre can be represented by place area as they are
usually smaller and more maintainable.

Additional tags:
- name=* - to facilitate handling
- admin_level=* - for linking to administrative borders, usually a
place area is inside an administrative area (debatable)
Other tags are not necessary since present on the linked place node.

Rationale for usage of boundaries:
- Larger settlements (probably from place=city on) cannot by
represented by a simple closed way (area) because this will be
unmaintainable and there is also the issue of a 2000-nodes limit per
way.
- The next solution would be Multipolygons. But they they do not
support other roles than inner/outer.
- The next solution would be a a relation type=place. But then mappers
will be tempted you use the edge of existing landuse=* areas members.
This would lead to wide-spread use/conversion of landuse=* to
multipolygons - which is a maintenance nightmare ("Multipolygonwahn").

The solution is to separate landuse and place areas. Although place
boundaries are only technically necessary for large settlements they
should be used for area representation on all place=* which have a
centre in order to have consistent tagging.

Detailed proposal with summary tables:
https://wiki.openstreetmap.org/wiki/Proposed_features/place_areas

Regards Joachim



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