[OSM-talk] Landuse areas etc. abutting highways

Dave F. davefox at madasafish.com
Tue Oct 6 14:39:48 BST 2009


Marc Schütz wrote:
> IMO (a) is the correct way to do this.
>
> We are trying to represent reality in our database.

I'm not sure that's true. A map is a representation of reality, not 
reality itself. With the tools available to us at the moment attaining 
reality is a lot of work For instance the majority of mappers don't draw 
an area for, lets say, an 1800mm wide pavement/sidewalk, they would use 
a linear way to represent it.

> In order to achieve this, certain abstractions are necessary.
>
> For a road, we can either choose to map it as a linear object (this is the common case), or we can map its geometry more exactly by using an area. In both cases, however, the object in our database represents the entire road (i.e. not only the middle line).

I Disagree
In the database a linear way /does /represent the centreline of the 
road. It's up to the renderer to decide how 'real world' it looks by 
deciding how thick to render that line.
If a) was used in this case the abutting area would overlap with the 
road render as it would be attached to the centre of the way.

>  Because in reality, there is no gap between the road and the areas next to it, there shouldn't be one in the database either.
>   

If you want to do real world with no gaps then whole road 
(highway,footpaths,verges, barriers etc) needs to be mapped.
Leaving a gap as in b) implies that the whole highway does have some 
width, it's just not been mapped yet.


> In other words, we should keep the topology intact, even if we choose to simplify the geometry.
>   
With option a) I think the topology is deformed inaccurately as it 
attached to the centreline of the simplified highway geometry.


Cheers
Dave F.
> Regards, Marc
>
>   





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