IMHO it's clear:
- a tag on a way describes that way, if it's a closed way and the tag is
describing an area, the tag matches the complete area inside that polygon.
- if a way is outer of a multipolygon and there are tags on the way,
these tags nevertheless describe the whole area, including all holes, as
it's still a tag on the (simple) polygon.
- if a way is inner of a multipolygon and there are tags on the way,
these tags describe the polygon described by this way.
- tags on the multipolygon relation describe the area represented by the
relation - that is all outer polygons minus the inner polygons.
If we follow this assumption, it's
1) not conflicting with double-tagging, which is in fact often useful.
Example: A big park with a lake in the middle of a big lawn.
- the whole area (including lawn and lake) is a park => the outer
polygon is tagged as a park
- only the small patch in the middle is a lake => the inner polygon is
tagged as a lake
- the whole area except the lake surface is a lawn => tag the
multipolygon as lawn.
Tags:
outer: {leisure=park}
inner: {natural=water}
mp: {landuse=grass}
2) it's unambiguous
Following Frederiks assumptions instead my tagging of the example above
would be interpreted as:
- area of the multipolygon (outer minus inner): leisure=park
- inner: natural=water
- whole area: no attributes (am I right?)
Thus the park is missing now (or Frederiks description is incomplete).
An even better example is one where the inner has a subset of the
multipolygon tags, let's say:
mp: {landuse=forest, wood=coniferous}
inner: {landuse=forest}
Frederiks assumption lead here to:
- mp: landuse=forest, wood=coniferous
- inner: untagged, as the tags are ignored because they don't differ
from the mp.
regards
Peter
Am 21.09.2013 17:00, schrieb Frederik Ramm:
> Hi,
>
>> The remaining question is, what should be the correct behavior?
>
> My assumption until now was:
>
> * If a multipolygon is untagged - where "untagged" means that it has no
> tags except a small list (type, source, source:*, note) then it will
> simply receive *all* tags from all (outer) member ways, but processing
> will fail if these tags differ in values.
>
> * If the multipolygon is tagged (with anything except type, source, note
> etc) then those are the tags for the polygon and way tags will not be
> looked at.
>
> * If the tags of the inner way differ from the tags of the outer way or
> the tags of the relation, except source, note etc., then the inner way
> will become a separate polygon.
>
> All this was without trying to make a judgement about which tags are
> "polygon tags" and which aren't.
>
> Bye
> Frederik
>
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