The Dictionary of Human Geography

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projection is readily understood as a two-stage

process that begins by shrinking the world to a

hypothetical globe, which establishes the

map’s statedscale. The second stage develops

an azimuthal, a conic or a cylindrical projec-

tion by transferring meridians, parallels, coasts

and boundaries on to, respectively, a plane,

cone or cylinder. Each of these three develop-

able surfaces has a distinctive grid of meridians

and parallels. Sometimes a third stage

readjusts locations and shapes, as when the

sinusoidal projection corrects for the enlarged

poleward areas on a cylindrical projection by

bending meridians inward towards a central

meridian.

Because of unavoidable stretching, com-

pression or shearing, map scale generally

varies from place to place across the projection

as well as with direction at a point. On a

cylindrical projection, for instance, scale in

the north–south direction might be constant

while east–west scale grows indefinitely large

near the poles. In general, scale will equal the

stated scale only at the point, line, or lines of

contact between the globe and the developable

surface. Moreover, distortion increases with

distance from the tangent point or standard

line, the location of which positions a zone of

comparatively low distortion. Allowing the

developable surface to penetrate the globe pro-

vides a ring of low distortion on an azimuthal

projection and two zones of low distortion on a

conic or cylindrical projection. A map author

can tailor a projection to a specific country

or region by carefully selecting the develop-

able surface and its orientation to the globe

(Robinson and Snyder, 1991; Canters, 2002).

Many perspectives and orientations are pos-

sible. Although all projections distort most

distances, an equidistant projection might

preserve true distance from the Equator, one

of the poles or some other point of interest.

Similarly, an equivalent projection can pre-

serve the true relative areas of countries and

continents, whereas a conformal projection,

which preserves small shapes as well as angles

around points, is especially useful on large-

scale maps of small areas. Unfortunately,

equidistance, equivalence and conformality

are mutually exclusive.

Because the mapped area of a country or

region can be seen as signifying its importance,

the well-known Mercator projection, which

significantly reduces the relative size of trop-

ical nations, has been attacked as biased and

eurocentric, with the most strident objections

emanating from proponents of the Gall–Peters

projection, an equal-area map touted as ‘fair

Cylinder

Cylindrical Cone Plane

Conic Azimuthal

map projection Principal developable surfaces (above) generate distinctive projection grids (below)

Gregory / The Dictionary of Human Geography 9781405132879_4_M Final Proof page 438 1.4.2009 3:19pm

MAP PROJECTION