Creating an example map

To better understand how the various parts of Mapnik work together, let's write a simple Python program to generate the map shown at the start of this chapter. This map makes use of the World Borders Dataset, which you downloaded in an earlier chapter; copy the TM_WORLD_BORDERS-0.3 shapefile directory into a convenient place, and create a new Python script in the same place. We'll call this program createExampleMap.py.

We'll start by importing the Mapnik toolkit and defining some constants the program will need:

import mapnik

MIN_LAT  = -35
MAX_LAT  = +35
MIN_LONG = -12
MAX_LONG = +50

MAP_WIDTH  = 700
MAP_HEIGHT = 800

The MIN_LAT, MAX_LAT, MIN_LONG, and MAX_LONG constants define the lat/long coordinates for the portion of the world to display on the map, while the MAP_WIDTH and MAP_HEIGHT constants define the size of the generated map image, measured in pixels. Obviously, you can change these if you want.

We're now ready to define the contents of the map. This map will...