[OSM-newbies] roads assocaited with towns.

[Craig Wallace]

On 25/05/2010 12:17, Trevor Hook wrote:

> My question is; how does Openstreet map know the lane is part of the
> village? I know my map is incomplete because I didn't map the connecting
> roads between Church Street and the main road, which itself is not
> connected to the POI Woodford. If I wanted to find a Church Street in
> Woodford how would openstreetmap (or any map based of OSM data) be able
> to process that request.
>
> Checking OSM, I've never seen a place name connected in anyway to a street.
>
> I can see 3 possible anwsers.
> *1) Geographical Proximity* -   what happens when a road is the same
> distance between 2+ place names
> *2) A Relationship* - I've looked in the wiki but didn't find anything
> appropriate for roads and place names, although it difficult to find
> stuff in the wiki unless I already know the name of the thing I'm
> looking for.
> *3) Place Boundaries* - Drawing a village boundary and everything inside
> is part of that village, I never done that but it would seem logical
>
> Should I be placing some sort of relationship/boundary on these roads?

Openstreetmap as such does not know what streets belong to what place. 
But various OSM based maps / services may figure it out in various ways.

Probably the most popular is Nominatim, which is the name finder on 
openstreetmap.org (what you get if you use the "Search" box).
It uses a variety of ways to figure this out (you can get more details 
at http://wiki.openstreetmap.org/wiki/Nominatim ).

The preferred option is definitely your number 3), ie draw an area for 
the boundary of the village (and town, city, county, country etc).
Though this isn't always practical, as the village might not have 
defined boundaries, or you may not know them.

Another option is to tag the streets with is_in:village or addr:village 
tag. This is helpful if you know a particular street is part of a village.

Though most villages don't have a boundary drawn, or streets tagged with 
is_in etc. So Nominatim has to base it on geographical proximity. But 
this is not very accurate, as it has to guess at the areas covered, and 
towns cover bigger areas than villages etc. Its unlikely for a road to 
be exactly the same distance between two places, otherwise part of it 
might be considered in one village, another part in the other.

If you use the search at http://nominatim.openstreetmap.org/ you can 
click the details option to see how an address was calculated, and the 
areas places cover. eg for Woodford (just based on the place node): 
http://nominatim.openstreetmap.org/details.php?place_id=8417375
Though note Nominatim hasn't been updated for a few months now.


Craig