The earth’s graticule and Projections 101
constant compass routes useful for navigators. A projection can also permit the car-
tographer to zero in on an area and present it in large scale.
There is no single best projection, although sometimes claims are made for new
projections that state they are better than any previously constructed projection. This
simply is not true. All projections have distortions, and a new projection merely has
distortions that are different from those of previously used projections. One can-
not even say there is a best projection for a particular use. From the infinite projec-
tions possible, there are usually several that could be used for any mapping project,
although if enough
conditions are specified, the choice can be limited.
While there are an unlimited number of projections and variations on projec-
tions possible, many of those already devised are not
in common use but remain
cartographic curiosities (Figure 6.10). Only about 25 or 30 projections and their
variations are widely used (see Appendix A).
The discussion that follows is a simplified and nonmathematical description of
projection concepts. Several excellent sources are listed in the Bibliography for those
who want a more rigorous treatment.
classification of Projections
Many attempts have been made to classify projections. Unfortunately, it is not pos-
sible to devise mutually exclusive categories since there is always some overlap. The
most common classifications are based on
projection properties and
projection sur-
faces.
Projection
Properties
It is desirable to preserve some of the geometric properties of the earth’s grid when
creating or using map projections. These basic properties and the projection types
that preserve them are as follows:
