(FIXME : label_spacing is still, too slow!!)
2. Re-use some agg objects.
3. placement_finder cleanups!
4. Added support for 'building_symbolizer' - extruded polygons
fs = m.query_map_point(x,y) # Map (screen) coordinates
for feature in fs:
print feature
TODO: provide interface to feature in Python, at the moment only __str__ implemented which dumps attributes