[OSM-talk] Zonal restrictions.
gdt at ir.bbn.com
Wed Apr 29 19:27:19 BST 2009
What currently comes closest to what I want is an area with a
place= tag, but the meaning of that is not clearly defined,
and you can't do everything with that.
I think what you really want is an implicit relation, where the road
ways inherit maxspeed from the relation, and you define the relation to
say that all ways in some area of some type should be in the relation.
I'm a little worried that this will get too complicated, but heading
down the path:
Define a polygon (er, closed way) to denote the area for which ways
get the inherited properties. I think this notion is just about tag
inheritance and not tied to any administrative boundary. For example,
in Mass in the US we have the notion of "thickly settled" (businesses
on both sides, houses close together) where the speed limit is 30 mph
and otherwise it is 40 mph. You could capture these with polygons to
save tagging time, but there is no defined district.
On the polygon put a maxspeed tag.
On the polygon put a special inverse_relation tag that somehow defines
how to match ways within the polygon that the maxspeed tag should
apply to. Sort of a SQL select statement :-)
Convince all the routing (and renderers that show speed?)
implementations to parse and use this new kind of inverse relation.
Plan B would be to add editor support to put maxspeed tags on all ways
of type 'highway=foo' that don't have them. So there'd be a lot of
tags, but maybe easy to add.
We might also want to encode maxspeed to record the rules, but also have
some typical_speed to record the speed at which traffic moves when it
isn't congested, extracted from tracklogs.
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