[Tagging] Places & admin boundaries

"Petr Morávek [Xificurk]" petr at pada.cz
Sat Oct 27 15:53:36 GMT 2012


I have a few questions regarding tagging admin boundaries and places. It
seems to me that these tagging schemes overlap a bit and I would like to
discuss it and possibly reach some kind of consensus about how to Do It

1) Polygon vs point for "Populated urban areas" (place=city, town...):
Current status: Overwhelming number of places (>90%) are marked by point
only, some have both polygon and point. The wiki says "A place can also
be defined using an area."
Having one object in the database twice (node+polygon) seems just wrong,
it's prone to errors (e.g. tags get easily out of sync), but...
Personally I think that both polygon and point are useful and neither of
them can fully replace the other. Polygon is useful for determining the
actual size of the place and what areas are considered to be "inside" a
settlement. Point is useful for navigation, rendering etc., especially
in case of places defined by more complicated (multi)polygons. It gives
the position of some kind of settlement centre (e.g. main square in the
village, historical/cultural centre in town), this is the place where
you expect to see the label on the map, or be navigated to if you input
only the name of the place without specific address in mind.
One solution I have seen is to define the area using boundary relation
and use the node as admin_center or label for it, but this is not always
possible (correct). The urban area itself is not always an
administrative unit, often it's only a part of larger administrative
unit that contains other non-urban areas as well.

2) Boundary relation or place=* for higher administrative units?
The overlap is especially visible in case of countries (but same
arguments apply for other units like states, counties, ...).
Majority of counties are in database represented twice - as node with
place=country and with admin_level=1 boundary relation.
This is again one real object represented by two completely distinct
objects in the database. Even though the common wisdom is that country
polygons are marked with admin_level=2 relations, most of the don't have
place=country tag. This is somewhat confusing - if I want to specify
currency, population etc. of the country, where should I put it? Node,
boundary relation, both?

3) As I've been writing this, I realize that what's bothering me are
basically two problems:
a) overlap between the use of boundary relations and place tag.
b) more general problem with point vs polygon tagging of POIs.

I would appreciate any thoughts and suggestions on these issues.

Best regards,
Petr Morávek aka Xificurk

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