[OSM-talk] is_in and similar tags

John Smith delta_foxtrot at yahoo.com
Wed Jul 29 02:45:45 BST 2009


--- On Tue, 28/7/09, andrzej zaborowski <balrogg at gmail.com> wrote:

> One of the two ways to indicate belonging to an area should
> not be in
> OSM, agreed.  Why's this the is_in tags, is the final
> rationale the
> space saving?

By using boundaries you can effectively tag every node, way and relation with is_in. If you were to tag everything there would be massive amounts of redundancy and wasted space.

> Take three villages belonging to some kind of
> administrative division.
>  You may need more than three nodes to draw a boundary that
> contains
> only these three nodes and no other nodes.  Then it
> depends on how
> much space a (repeated three times) tag takes in your
> particular
> format compared to space taken by a separate node + the way
> with a
> couple of member nodes.

You seem to think this is just about place nodes, it's about everything inside a boundary.

> Or as a less practical example take two ways that cross one
> another
> (one may be a bridge or tunnel), one officially belonging
> to county A
> or postcode A and the other to B.

Exactly, you wouldn't need to split the way, by having a boundary it could be calculated which part would be within which area.

At present there is already boundaries for at least countries, some have states and out boundary information. Which is a nice start and so it's not like we're starting from nothing here.


      




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