[OSM-talk] Mapping huge lakes as coastline

[Michal Migurski]

On Apr 14, 2011, at 1:52 AM, Jukka Rahkonen wrote:

> Teemu Koskinen <teemu.koskinen <at> mbnet.fi> writes:
> 
>> 
>> I converted a few of the biggest lakes in Finland a few years ago to 
>> coastlines, and they worked fine, until last year some other user converted 
>> them to multipolygons with natural=water -tags. He also splitted the biggest 
>> lake (Päijänne) in pieces, which created arbitrary lines across the lakes at 
>> random where the lake was divided to different polygons.
>> 
>> The biggest lakes in Finland have tens of thousands (or even hundreds of 
>> thousands) nodes and a LOT of islands, so it's not practical to represent them 
>> as (multi)polygons IMO.
> 
> It is not practical, either, to represent them as coastlines. For example
> osm2pgsql is not importing coastlines into PostGIS at all but users must use the
> processed land polygons as shapefiles for rendering these coastline lakes. One
> may say it works fine with Mapnik rendering because of this shapefile
> workaround. Some could call it as a dirty hack. For example, it gets complicated
> when somebody wants to add tags for the lakes and islands.


FWIW, Dane added a --keep-coastlines flag to recent versions of osm2pgsql. It hasn't fully propagated out to various package managers and things, but it's a big help in these situations.

-mike.

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