It will suffice therefore to point out that the ordinary needs of the cartographer can be met by conical projections, and, in the case of maps covering a wide area, by Lambert's equal area projection.
The Measurement of Areas is easily effected if the map at our disposal is drawn on an equal area projection.
When dealing with maps not drawn on an equal area projection we substitute quadrilaterals bounded by meridians and parallels, the areas for which are given in the " Smithsonian Geographical Tables " (1894), in Professor H.
the rings are at first of nearly equal area.
Let us conceive the zone in question to be divided into infinitesimal rings of equal area.