Cartopy is a library, written in python, which utilises the power of Proj.4 in a pythonic way. The simplicity of the interface to Proj.4 is extended in order to build maps easily with Matplotlib.
Note
Cartopy is not currently operational. If you wish to contribute to this project, please get in touch. Alternatively, the Basemap extension to matplotlib is a finished package with a subset of the functionality planned for cartopy.