On to cascaded unions for Shapely ...
>>> from osgeo import ogr >>> from shapely.wkb import loads >>> ds = ogr.Open('/Users/seang/data/census/co99_d00.shp') >>> co99 = ds.GetLayer(0) >>> counties =  >>> while 1: ... f = co99.GetNextFeature() ... if f is None: break ... g = f.geometry() ... counties.append(loads(g.ExportToWkb())) ... >>> len(counties) 3489
Matplotlib makes a pretty picture of those 3489 polygons:
Shapely never had the power to dissolve adjacent polygons in a collection before, or at least not over large collections of real-world data. GEOS 3.1's cascaded unions are a big help:
There's user interest in leveraging the new reentrant API in GEOS 3.1, and releasing the GIL when calling GEOS functions to improve performance in multithreaded apps. I'm all for it.