Mapnik: SVG output not working

Question

I want to generate SVG maps in Python using Mapnik 3.0.13 (built from source). I'm using version 3.0.13 of the Python bindings as well, built with PYCAIRO. My code:

f = open('/tmp/test.svg', 'w')
surface = cairo.SVGSurface(f.name, map.width, map.height)
mapnik.render(map, surface)
surface.finish()

The output SVG file looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="4961pt" height="3508pt" viewBox="0 0 4961 3508" version="1.1">
<defs>
<image id="image3198" width="20671" height="14617" xlink:href="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAUL8A ...

Followed by ~200 MB of base64-encoded PNG garbage.

I tried recompiling my library and bindings to use the native svg_renderer instead of Cairo, but got the same result.

How do I get a "real" SVG? This is just a PNG file wrapped inside an SVG (in an extremely inefficient way).

Accepted Answer

I created a Mapnik issue for this: https://github.com/mapnik/mapnik/issues/3749

Turns out this happens when your style uses compositing operations like comp-op="multiply". These lead to rasterization of the map.

Removing all comp-op filters produces a "real" SVG. Alternatively, PDF output works as mentioned by @knowname above.

Answer 2

The problem has been found to be something with SVG version support. You can build Mapnik with this patch applied:

https://github.com/mapnik/mapnik/pull/4029#issue-251451960

or just use python-cairo with a code like:

surface.restrict_to_version(cairo.SVG_VERSION_1_2)

See also https://help.openstreetmap.org/questions/65497/is-there-any-change-in-svg-exports/67940

Mapnik: SVG output not working

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