Because the Earth is a sphere, any representation of its surface
on a flat sheet of paper involves distortion. This distortion is
relatively insignificant for maps showing small parts of the
Earth, such as city maps, but quite considerable for maps of
whole countries or continents. The decision facing a map-maker,
therefore, is not whether to have a distortion on a map, but
what type of distortion. Over the centuries, various geometrical
schemes have been worked out for representing the curved surface
of the Earth on map sheets; these schemes are known as map
projections. All projections have certain advantages and
disadvantages, and the selection of one or the other depends
chiefly on the needs of the user. The size and shape of the
country being mapped determines the most suitable projection for
its system of topographic maps. Very large countries such as
Canada must be divided into strips, usually called zones, which
are projected onto a plane in orderly fashion. One such system
of strip projection is the