[OSM-dev] Relation - Multipolygon = "Area"

[Ben Supnik]

Hi Frederik,

On 4/19/11 4:13 AM, Frederik Ramm wrote:

> You explain "building=yes" as meaning "is it filled?", when in reality
> it is completely up to the renderer whether or not to fill an object
> that is tagged to be a building.

Wait, I don't think I agree with this.  That is, to me, the question of 
whether a 'thingie' in OSM is an area thingie or a line thingie should 
_not_ be up to the visualization layer.  I think I am one of many voices 
who are saying that we should 'fix' this.  (I'm not saying anything that 
isn't on the wiki already here.)

My concern here is that there are geometric operations you might want to 
do to "OSM data" without being dependent on interpretation, and you 
can't always do them if you don't know what you have.  Consider tiling 
the data.  If a way is a linear ring surrounding my tile, I can drop it. 
  If it is a polygonal area/point set, I need to crop the point set to 
the bounded area.

It also seems difficult to provide a 'generic' editor (an editor not 
specifically tied to a visualization schema) without knowing whether a 
closed ring is an area or line loop.

This is a problem we do not have with multipolygons (they're always 
areas) and we certainly do not have with ways vs nodes...just with the 
special case of close ring rings being areas sometimes.

So Frederik, I agree that the data model, editing and rendering are 
distinct.  But I would like to see the pure 'spatial' interpretation of 
data be unambiguous in the data model, even if its visualization is 
highly subjective.

cheers
Ben


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