[OSM-talk] [Talk-us] NHD Dataset

Frederik Ramm frederik at remote.org
Mon Feb 16 20:20:56 GMT 2009


Christopher Schmidt wrote:
> So, to be clear, what this looks like to me is that for any polygon, you
> can take the 'one long way' that would previously have outlined it, and
> instead of having that 'one long way', you have as many little ways as
> it would take to make up that ring. So, for a 4,005 node way, assuming
> a 1,000 node limit, you could have:
>  * 10 1,000 node ways
>  * 1 5 node way

That's the idea.

> However, it is not clear that that is what Frederik meant in: 
>   http://lists.openstreetmap.org/pipermail/talk/2009-February/034091.html
> He suggested that the ways should be split up into smaller 'ways of
> managable size', but from what I've seen, these 'ways of managble size'
> are often closed polygons on their own:

They are today, for practical reasons, but this is really not encouraged 
as it may lead to ugly border lines in the middle of areas.

> Maybe Frederik was saying that the former is okay. My curiousity in that
> case is just if renderers -- especially Mapnik -- will actually support
> these things. (I can't imagine it working for osmarender, but that is
> less concenring to me.)

The JOSM build-in renderer already supports them, and there is a patch 
for Osmarender that does. And with so many bright minds at work on 
Mapnik it can only be a question of time until Mapnik supports that kind 
of relation as well. (The fact that, for stability, you should not rely 
on correct ordering of the relation's members even though 0.6 supports 
ordering makes things a *little* more difficult to process, but 
requiring correct ordering of editors and mappers would probably 
introduce too many errors.)

There really is not much other choice, as areas grow larger and the old 
idea of simply drawing touching polygons relies on a rendering style 
without a "casing" around the polygon.


Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"

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