mapnik/mapnik — pull request #2481 by strk (2014-10-02 13:26:46+00:00)
Title: Add geometry_display_expression parameter

It can be used to run arbitrary functions to preprocess the geometry
to be rendered based on pixel resolution and/or bounding box.

Includes testcase

This parameter makes the "simplify_geometries" one unneeded, and avoids having to add more parameters for different combinations of clipping/gridding/simplification (as seen in #2459)