Authors: Eligio Maure, Blessing Kamwi

5. Working with Map Projections in Python#

5.1. Overview#

The representation of a portion of the Earth on a two dimensional planar surface leads to distortion of one form or another that often requires some transformation of the round surface to a plane denoted projection [Snyder, 1987, Snyder and Voxland, 1989, Usery et al., 2009]. Simply put, a map projection is a systematic representation of all or part of the surface of a round body, like the Earth, on a plane. This representation often includes lines that delineate meridians and parallels, depending on the definitions of a map projection [Snyder and Voxland, 1989]. To perform operations with geographic data, such as overlays or accurate spatial/temporal analysis, a common coordinate framework is required; map projections introduce transformations that allow the creation of such common frameworks. The techniques involved in these transformations use some kind of a coordinate system. Geodesy is the mathematical treatment of these transformations. Together with geodesy, map projections allow the representation and visualisation of the transformed spherical or ellipsoidal form of the Earth’s surface to a two dimensional representation.

This chapter gives a brief outlook of map projections, the associated transformations between different projections and the advantages and limitations of working with different projections. We will briefly discuss a few important concepts associated with geodesy and coordinate systems prior to the discussion of map projections. As discussed in Section 3, Cartopy is the common package used in Python to work with imagery that requires a map projection. Matplotlib provides the visualisation capability.

5.2. Learning Outcomes#

  • Gain familiarity with cartographic transformations

  • Gain ability to visualise satellite scenes on a map

  • Gain ability to convert a given map projection to another based on the use case

5.3. How to Proceed#

This chapter assumes familiarity with materials of A Brief Introduction to Python.