[OSM-dev] Coastlines and water - contact and technical

[Jon Burgess]

On Sun, 2009-07-19 at 16:10 -0400, Ben Supnik wrote:
> Hi Jon,
> 
> Jon Burgess wrote:
> > This is how the data appeared when the existing polygons with holes were
> > run through the 0.4->0.5 conversion process. In 0.4 they consisted of a
> > single tagged way with disjoint segments. In the conversion, the
> > disjoint segments turned into multiple tagged ways and a relation was
> > created with them all as members. The conversion process was not
> > intelligent enough to assign them roles.
> 
> Does that create rendering errors?  

It probably does in some renderings.

> (E.g. holes not being rendered as 
> holes?)  Or are clients somehow figuring out that the holes are holes 
> via a heuristic?

You would need to examine each of the clients to understand whether they
cope with this or not.

> Sorry to beat this to death here...it looks like clients have to handle 
> a number of special cases for legacy data...I want to make sure I get 
> them all so that my shapefile output isn't grossly different from what 
> users see on the map.

Well, this specific case of having tags on the inner ways is probably
disappearing. I believe someone wrote an automated tool to 'correct'
this data some time ago. Even so, you sometimes need to know the history
to understand why some of the things are the way they are.

One obvious comparison you could do would be to compare the shapefiles
to those generated by osm2shp or osm2pgsql+pgsql2shp.

	Jon

> cheers
> bne
> 
>