Creating a custom proj4 spatial reference string

If you are not able to find the spatial reference system that you need in the standard list, or if you have a specialised SRS (e.g. local grid) that you need to define, then you will need to create a proj4 string.

For many well-known spatial reference systems, a good resource is the spatialreference.org or epsg.io website. You can use this site to search for the SRS that you need, and then request the proj4 string from the list of links. The website will usually give you a number of alternatives, so be sure to choose the correct version, including the units and the datum.