[mkgmap-dev] Address search and index.

Wed Feb 16 19:39:24 GMT 2011

>>> It should be easier to maintain than
>>> the coastline data because the political (or adminstration??) bounding
>>> polygons should obey certain rules that could be checked automatically.
>> Can you give an example? I don't see why it should be easier than
>> coastline checking.
>>
>
> 1) A bounding polygon ought to form a closed way. Coastlines seem to be
> composed of many open ways that happen to share end-points (more like
> roads). That latter fact makes it harder to check a coastline since a
> "way" flagged as "coastline of France" will at some point share
> endpoints with a "way" flagged as "coastline of Spain", and that's true
> but not checkable automatically.
>
> 2) A bounding polygon's name ought to be unique within its own parent
> bounding-polygon. If for some reason you really want two
> bounding-polygons to be disjoint, but refer to the same logical place,
> you'd put them both in a "relation".
>
> 3) There should not be an intersection of two bounding polygons at the
> same level. In other words, two towns can't intersect.
>
> 4) There are such things as cities that span multiple counties (like
> London, England for instance). There needs to be rules to allow that,
> maybe where the bounding-box for the majority of the county of Middlesex
> is required to be entirely outside the bounding box for London, but a
> second bounding-box (also flagged as 'county of Middlesex') is placed
> inside the bounding-box for London, but a member of a "relation" with
> the other Middlesex to prove that they are supposed to be the same. If
> the 'relation' was omitted, the auto-checkers would barf because you'd
> have two disjoint places called Middlesex inside the same parent
> bounding box (England). (You might choose to relax that rule if the two
> Middlesex bounding-boxes shared one or more periphery vectors, as they
> would here.)
>
> 5) The "political:layer" tags should increase in value as the
> bounding-boxes nest. In the unusual case of enclaves that I mentioned in
> my earlier post, you allow the layer value to break that rule (within
> the enclave the inherited knowledge of the parent bounding boxes is
> forgotten), but there has to be a tag to say "political:enclave=yes" or
> something to let it happen without the auto-checher barfing.
>
> 6) Er - there must be more!

I don't understand, sorry.
I think you assume that boundary information is stored as single 
polygon. This won't be accepted by the OSM community and is not how 
boundaries are tagged at the moment. Larger structures are realized as 
multipolygons. This makes sense because a national border is always a 
border of a county and a city etc. And editors like JOSM don't need to 
download the complete border of two countries just because you want to 
edit a small street crossing the border.
Please have a look at the 
http://wiki.openstreetmap.org/wiki/Tag:boundary%3Dadministrative and 
http://wiki.openstreetmap.org/wiki/Relation:boundary pages. Most of your 
ideas are already described there and can be found in the OSM data.

As a result you have a bunch of lines and some polygons both for 
coastlines and for boundaries. You need to connect the open lines 
(boundaries use the multipolygon information to do this). In the end you 
have uncomplete data where you have to close some polygons 
automatically. There no substantial difference between coastline and 
boundary proessing.

WanMil