Visualizing geospatial data
It's very hard, if not impossible, to understand geospatial data unless it is turned into a visual form—that is, until it is rendered as an image of some sort. Converting geospatial data into images requires a suitable toolkit. While there are several such toolkits available, we will look at one in particular: Mapnik.
Mapnik is a freely-available library for building mapping applications. Mapnik takes geospatial data from a PostGIS database, shapefile, or any other format supported by GDAL/OGR, and turns it into clearly-rendered, good-looking images.
There are a lot of complex issues involved in rendering images well, and Mapnik does a good job of allowing the application developer to control the rendering process. ...