7.5 Which CRS to use?

Same: no good answers!

-> Use the right one for every task

If it is a geographic: the default is “EPSG:4326”

7.5.1 Projected:

• Use the one that the public mapping agency use (In France “EPSG:2154”)

• UTM: for relatively small area (less than 6 degrees in longitude), you will have a distorted area farther you go from the center of UTM.

• You can use https://crs-explorer.proj.org/

You can pick:

• Conformal: preserving angles -> same shapes

• Equal area: keep area the same: good for density

• equidistant: preserving distance

• a mix of the above

The goal will be to minimize distortion.

Authors recommendations:

• Lambert Azimuthal Equal Area (LAEA): same size but distorted shape

• Azimuthal equidistant ([AEQD]https://en.wikipedia.org/wiki/Azimuthal_equidistant_projection)): accurate line distance between a point and the center point of the local projection

• Lambert Conformal Conic (LCC): good if you are away of equator

• Stereographic (STERE