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.
Let us conceive the zone in question to be divided into infinitesimal rings of equal area.
The area of a rectangle, for instance, is found by calculation from the lengths of the sides, not by construction of a square of equal area.
The Lancashire coal-field, and the portion of the bounding plain between it and the seaport of Liverpool, contain a population greater than that borne by any equal area in the country, the county of London and its surroundings not excepted.
