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I am currently generating tiles based on OSM data using Mapnik and Python and am quite happy using the XML styling but I am at a loss as to how to vary the styling on an element by element basis.

I would like to render OSM map tiles where certain elements are styled according to their attributes, for example, a roads colour is based on its length, or an area is coloured based on its size.

Is this possible?

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up vote 1 down vote accepted

If you use a Postgis database with osm2pgsql data scheme, you have a column way_area for polygons. Unit is square degrees or google meters, which is only at the aequator eqivalent to real metres:

For the length, I guess you have to calculate it on your own. But keep in mind that a road may have been broken up to reflect route relations diverting or joining.

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Thanks, my main issue is with how to change the styling of the rendered item based on way_area or another variable. Currently I can only define the style that applies to all ways or all areas etc. – StuGrey Jan 16 '13 at 12:23
The Style "area-text" has a good example: <Filter>[way_area] &gt;= 80000 and [way_area] &lt; 150000</Filter> – AndreJ Jan 16 '13 at 12:59
Excellent, so if for instance I wanted to vary colour by size in small increments I would have to create a <filter> for each increment? I guess this is the way to do it if there is no way to directly base a colour on variable. The downside is that the style file could get very large. – StuGrey Jan 16 '13 at 13:09
You are right. The size of the style file is no problem: Every rule that does not fit simply gets skipped. – AndreJ Jan 16 '13 at 13:48

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