Compute the geo grid unit area induced by the Mercator projection at the location of the Eiffel Tower:

A small square of side length 0.01 in projected coordinates has the following area:

Draw the square:

Compute the geo grid unit area at your geo location for the "VanDerGrinten" projection:

These are the default values of the parameters of the "VanDerGrinten" projection:

Specify other values for the parameters of the projection:

Specify a location using a pair {lat,lon} in degrees:

Use locations with geo position heads:

Specify a location using a geo Entity object:

Compute the geo grid unit area for a list of locations:

Convert the QuantityArray output into its normal form:

GeoGridUnitArea can efficiently process values for large numbers of locations:

For a cylindrical projection, the projected unit area only depends on latitude:

Use GeoGridUnitArea to approximate the geo area of a small region using the projected area in a map:

Project with the Albers projection and compute the flat map area:

Multiply the result with the geo grid unit area at some central location of the region:

Compare with the correct value of the geo area:

Compute the geo area of a region defined on the projected map:

Compare with a computation based on a polygonal approximation of the disk:

Take a location and a projection:

Construct a family of projected squares of decreasing size, converging to that location:

Compute the ratios of an unprojected area over a projected area for those squares:

The values converge to the value given by GeoGridUnitArea for that projection at that location:

The projected unit area varies with the square of the geo model size:

The projected unit area varies with the inverse square of the reference model or the central scale factor:

Equal-area projections have constant geo grid unit area over the globe:

For a random set of locations across the world, check that ranges of projected unit area have zero width:

If a geo location cannot be projected, then the projected unit area cannot be computed for that location:

This location is not on the half-Earth covered by the "Orthographic" projection with a default center: