[mkgmap-dev] render closed waterway polygons?

Thu Oct 25 14:21:08 BST 2012

In my styles, I want to render closed waterway polygons as areas by using the continue statement in my lines:

waterway=canal & natural!=water   [0x1f resolution 23 continue]

polygons file:

waterway=canal  [0x3c resolution 23] 

Those closed bodies are rendered ok now, filled with water. If this waterway area consists of two or more separate ways, connected to each other,
this is not rendered as water polygon but only as linear elements, which is excellent.

Problem arise at the tile borders, where I get unwanted side effects, linear elements of waterways that cross the tiles are automatically closed by mkgmap and therefore rendered as areas (filled up with water), which I do not want. I like to distinguish those artifical polygons in my style file from the really closed waterway polygons. Are those artifcially closed polygons tagged internally by mkgmap somehow, so I can exclude them from my polygon style?

Background:
In the Netherlands there are tons of areas of water tagged as waterway=* (canal, drain, river).
According to the wiki this tagging is wrong (for polygons natural=water should be used, or for bigger rivers, waterway=riverbank).
But since Potlatch, Josm and Mapnik automatically render closed waterways as areas, many mappers are making this mistake.
(One could argue if maybe the wiki should be revised, why is only waterway=riverbank a polygon and a closed body of waterway=river not?)

In Potlatch all natural=water polygons are called "Lake" so many mappers want to 'improve' those areas by tagging them as waterways.
I have tried to contact the Potlatch developers about this issue but they dont seem to care to adjust it.