subject and Purpose of the map




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Judith A. Tyner. Principles of map design. New York. „The Guilford Press”, 2010

subject and Purpose of the map
The subject and purpose of the map are the most critical factors for picking a projec-
tion. For distribution maps, equal-area projections should be used; for maps show-
ing world distributions, a nonequivalent projection will usually be misleading since 
quantity and area are related (Figure 6.38). When the distribution is illustrated by 
dots, the impression of the relative density of the distribution will be distorted if non-
equivalent projections are used.
For navigation, maps that show angles or azimuths properly are needed; still 
other needs might dictate equidistance or conformality. Appendix A will aid in the 
selection of a suitable projection. The USGS has created a poster of map projections 
and their properties (see Appendix B).
size and shape of the Area
As we have seen in the previous discussion, some projections are best suited for areas 
of great east–west extent, others for north–south areas. Reversing these would result 
in serious distortion within the area mapped. The area of interest should always be 
placed in the zone of least deformation. Therefore the cartographer should be famil-
iar with those zones for the commonly used projection groups.
For small areas (large-scale maps), the choice of projection is seldom of any con-
sequence, since at this scale the differences between projections are negligible. A 
map of a city or county will look essentially the same on any projection. (There are 
occasions when projection must be taken into account for small areas, but these are 
usually of more concern to surveyors than to thematic mapmakers.)
For world projections, the size and shape of the area will determine if an inter-
fIgURe 6.38. 
Greenland and Mexico have the same number of dots, but the conformal pro-
jection gives an erroneous impression of density.

The earth’s graticule and Projections 125
rupted projection should be used and where the interruptions should be placed. 
Obviously, if the distribution being mapped extends over both land and water, an 
interrupted projection will not be suitable; if the distributions are confined to land, 
placing interruptions in the ocean areas would be appropriate.

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