[OSM-talk] Mapping everything as areas

[Morten Kjeldgaard]

On 25/11/2009, at 14.11, Jean-Marc Liotier wrote:

> Ævar Arnfjörð Bjarmason's diary entry last week (http://j.mp/8ESP8o)
> stired my interest. Using a few examples, he showed how mapping
> everything as an area - or as a volume - makes ultimate sense.  
> Should we
> go for it now ?

Talking about roads:

I don't see the point mapping roads as areas. There's not much you do  
with an area that can't in principle be done using a line with  
appropriate tagging. The problem is that the current tagging namespace  
is too simple and not expressive enough to allow it. For example, if I  
write

   highway=residential cycleway=track width=3

there's no way for you to know if "width=3" describes the cycleway or  
the road itself.  In my view it would make much more sense to work on  
a more expressive (perhaps BNF based?) tagging scheme. This would  
enable a gradual enhancement of the map, where the new tagging syntax  
could live along-side the old.

Areas are reminicent of the "map-drawing" approach to the map, in the  
sense that mankind has been drawing maps  with paper and pencil for  
thousands of years.  The "map-drawing approach" is valuable in OSM  
because it allows us to indicate residential areas parks, etc.   
However, in addition, OSM has a graph-based approach for a description  
of the network of roads which makes it *uniquely* valuable. Graphs  
prefectly represents the road map and can be used for many  
applications, routing is an example that many people use daily.

Conversely, there isn't much you can do with graphs that can't be done  
with areas, and since the "map-drawing" approach has great appeal to  
people enjoying beautiful and detailed maps, the pressure for  
deprecating the graph-based approach in favour of the map-drawing  
approach will be ever increasing.

We need to resist that. Let's not throw out the baby with the bath- 
water!

Cheers,
Morten