Friday, August 27, 2010

Mapnik label cut off strategies

I've been spending a lot of time dealing with mapnik labels/shields being cut off. Here are some strategies:

  1. change the "buffer_size" property of the map object in the mapnik xml ... you can also direclty change this in generate_tiles.py (which comes with osm mapnik package). I don't think the mapnik xml was being read in my case. When I changed the line self.m.buffer_size to = 0, my cutoff problems disappear
  2. you'll need to do some tweaking with the order layers are defined within mapnik/cascadenik
  3. also tweaking of text-allow-overlap and text-avoid-edges (these are cascadenik properties, there are similarly named ones for mapnik alone)
  4. you may need to merge segments of the same road
To sum up: my strategy was first getting all my ordering straightened out with how layers are defined/ordered within mapnik/cascadenik. I then turned most layers to text-avoid-edges and text-allow-overlap to true. I set the buffer value to 0 in the .py file that I was using to render my tiles (in the osm package). Then moving around stuff that overlapped badly and will possibly need to merge segments of the same road.
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