pyproj

PyProj is a Python library that provides bindings to the PROJ cartographic projections library. It enables users to define coordinate reference systems, convert coordinates between CRSs, and perform geodetic calculations necessary for map projections, data reprojection, and spatial analysis.

The library exposes a Pythonic API built around core concepts such as CRS, Transformer, and Geod. The CRS class represents a coordinate reference system, while Transformer handles coordinate transformations between two CRSs, accommodating single points or arrays. The Geod class performs geodesic calculations on the ellipsoid, enabling forward and inverse navigation calculations.

PyProj supports EPSG-based CRSs, WKT2, and Proj strings, and can read or construct CRS definitions from these representations. It can also compose transformation pipelines to apply multiple steps in a single operation. Transformations can be performed for scalar coordinates or large arrays, with options to control axis order and output formats.

Development and ecosystem: PyProj originated as a Python wrapper around PROJ and is maintained by an open-source community. It requires a PROJ installation and is widely used in geospatial workflows and libraries such as GeoPandas and Rasterio.

See also PROJ, CRS, Transformer.