Cartopy developer interfaces#

Cartopy exposes several interfaces to help make it easier to add new functionality quickly and easily.

Data/Download API#

In order to keep the size of a cartopy release low, the majority of data is not included as standard. This means that, when developing new features, it is often necessary to provide interfaces which can acquire data from external sources (normally via HTTP). The Downloader class has been designed to make this process as easy as possible for developers to extend, whilst still making it possible for users to configure in their own way.

An example of specialising this class can be found in which enables the downloading of zipped shapefiles from the website. All known subclasses of Downloader are listed below for reference:

Raster images#

The abstraction between retrieval and visualisation of raster data means that the class exists to retrieve an image (given sufficient context of projection, extent, resolution etc.) while in the matplotlib interface the cartopy.mpl.slippy_image_artist.SlippyImageArtist class feeds the appropriate information to the RasterSource and visualises it on a map. The orchestration in Matplotlib is made more convenient to the user of a GeoAxes through the add_raster method. Anything which exposes the validate_projection and fetch_raster methods in the form described in RasterSource can be used as a slippy maps source in this way.

The SlippyImageArtist class provides panning and zooming of image sources which are able to re-retrieve data (such as that from a web service) for efficient and interactive visualisation. Generally the SlippyImageArtist is a developer’s interface, with users often creating a SlippyImageArtist instance through the GeoAxes’ add_raster() method.