Shape factors are calculated from measured dimensions, such as diameter, chord lengths, area, perimeter, centroid, moments, etc.
The dimensions of the particles are usually measured from two-dimensional cross-sections or projections, as in a microscope field, but shape factors also apply to three-dimensional objects.
A shape factor equal to one usually represents an ideal case or maximum symmetry, such as a circle, sphere, square or cube.
The less-common elongation shape factor is defined as the square root of the ratio of the two second moments in of the particle around its principal axes.
Such an estimate on a typical flat map, using the Mercator projection, would be less accurate due to the distorted scale at high latitudes.