Proj4 Projection Specification

As of version 5.0 projections are now specified using Proj4 syntax. Proj4 is a widely used open-source programming library for managing map projections. It defines a compact, single line syntax for specifying a map projection.

The easiest way to get a Proj4 projection string is to look it up in a specialized projection search service. Two are currently available:

• epsg.io
• spatialreference.org

Examples:

Massachusetts State Plane (feet)

+proj=lcc +lat_1=41.71666666666667 +lat_2=42.68333333333333 +lat_0=41 +lon_0=-71.5 +x_0=200000 +y_0=750000.0000000001 +ellps=GRS80 +datum=NAD83 +to_meter=0.3048006096012192 +no_defs

UTM Zone 18 North

+proj=utm +zone=18 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs

Web Mercator

+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs