Iris
The Iris library implements a data model to create a data abstraction layer which isolates analysis and visualisation code from data format specifics. The data model we have chosen is the CF Data Model. The implementation of this model we have called an Iris Cube.
Iris currently supports read/write access to a range of data formats, including (CF-)netCDF, GRIB, and PP; fundamental data manipulation operations, such as arithmetic, interpolation, and statistics; and a range of integrated plotting options.
Cartopy
Cartopy is a Python package designed for geospatial data processing in order to produce maps and other geospatial data analyses.
Key features of cartopy are its object oriented projection definitions, and its ability to transform points, lines, vectors, polygons and images between those projections.
You will find cartopy especially useful for large area / small scale data, where Cartesian assumptions of spherical data traditionally break down.