[OSM-dev] Defining the area of a country / What country is a LatLon in.

[Marcus Wolschon]

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Dear Robert, and Andy,

Robert: why did you send a "I think we should" and "or something"
only to me instead of the list? I cannot decide alone
on such matters. Thus I'm asking for a consense on the list.

Marcus

>> How am I to
>> a) get all border-pieces without downloading all of the planet.

Andy wrote:
>Best to download the planet, that way you'll get them all.

Sorry, there is no space nor bandwidth to do this. This is
not possible at all.
I guess
http://wiki.openstreetmap.org/index.php/OSM_Protocol_Version_0.5#Searching_for_Objects_by_Tag
can be used here.



>> b) interpret them (they may be incomplete e.g. in the baltic see).
>>
>> We have a defined tag "place=country;name=XXX" and it makes no

Andy wrote:
> Is this for nodes? In which case it's necessary, since it's the easy
> leg up to putting a country on the map without needing an entire
> border for it. We don't like high barriers to entry.

No, as stated in the wiki place= is for nodes AND for areas.
For nodes it clearly denotes the center, for areas it clearly
denotes the polygon.


Andy wrote:
> a) Starting with the world_boundaries shapefiles, set up a mechanism
> to detect which country a given point (or lat/long) is in
> b) Then come up with a mechanism to use the boundaries in OSM, which
> bears in mind that the shapefiles are inaccurate but complete, and the
> OSM boundaries are (potentially) more accurate buy woefully incomplete

Where do I get this "world_boundaries"-file, how big is it?
It does not sound worth the effort instead of taking the borders
in OSM and combining them in a machine-readable format.

Robert wrote:
> Most borders are between 2 countries, not just one. I think what we need
> is to draw border ways between countries, and tag them just as
> border=country or something,

We are alread doing this as
boundary=administrative and "right|country"=XXX and "right|country"=YYY.
Thus there is no "we need to" and no "or something".


> then have a relationship defining the
> country with all it's sections of border and possibly a node near the
> middle that represents where the country's name should be drawn.

Okay. Please let us specify that relation.
I think the center-point should be optional.

* Are the related ways to be ordered or unordered?
<relation id="???" name="border:country>
 <member type="way" id="2" role="border_100"/>
 <member type="way" id="???" role="border_200"/>
 <member type="way" id="???" role="border_210"/>
 <member type="way" id="???" role="border_300"/>
 ...
optional: <member type="node" id="111" role="centerPoint"/>
</relation>

<node id="111">
 <tag key="place" value="country"/>
 <tag key="name" value="Germany"/>
 <tag key="right" value="country"/>
</node>

<way id="222">
 <tag key="place" value="country"/>
 <tag key="boundary" value="administrative"/>
 <tag key="right|country" value="Germany"/>
</way>

* no consecutive numbers to allow later spliting/insertion of ways
  without renaming everything
* if the way and the relation disagree on the country-name, the
  relation is used.

Questions to the list:

? What algorithm should be applied to build the polygon of all
  borders?

? How to detect and how to deal with incomplete=unclosed resulting
  border-polygons?

? How to deal with illegal polygons (ways inserted 2 times,
  unconsequtive ways, contained closed ways)?

Using a simple closed polygon with "place"="country" and "name"="XYZ"
does not have these problems but border-lines cannot be shared.

Marcus

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