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

[M∡rtin Koppenhoefer]

2011/4/19 Igor Brejc <igor.brejc at gmail.com>:
> On Tue, Apr 19, 2011 at 3:15 PM, Jukka Rahkonen
> <jukka.rahkonen at latuviitta.fi> wrote:
>> ...Which brings to my mind another
>> smallish problem with big real world area features which has been splitted
>> to smaller areas so that they can be handled in OSM. If you want to render
>> them with fill and outline the split lines come visible on the map.
> For high quality rendering, the rendered would have to join such areas
> together before drawing the outline. A typical example are
> waterway=riverbanks - if you want to render blue riverbank outlines, you
> need to join the areas together.


but it is currently often completely unclear from the data, whether it
is several smaller independent entities of the same type, which share
some borders, or whether it is one big entity split up for handling
issues.

The riverbank example is an nice one what can go wrong IMHO. You
shouldn't tag waterway=riverbank for arbitrary pieces of ways crossing
the river (at least not if you wanted to express "this is a riverbank"
--- I know, it's all about conventions, and, there is at least 2
current proposals to overcome this specific ontologic inconsistency
(one is refining natural=water and the other a new relation type
"area")).

As a side note: also when joining the areas you will at least get on
ugly line where the river meets the sea (which you could avoid with
the area relation).

cheers,
Martin