Rarely used by some commercial tile providers. Uses Elliptical Mercator projection.
The most common CRS for online maps, used by almost all free and commercial tile providers. Uses Spherical Mercator projection. Set in by default in Map's crs option.
A common CRS among GIS enthusiasts. Uses simple Equirectangular projection.
A simple CRS that maps longitude and latitude into x and y directly. May be used for maps of flat surfaces (e.g. game maps). Note that the y axis should still be inverted (going from bottom to top).