The Mapmaker's Choices
So anyone wishing to create maps better than a simple sketch must face a series
of decisions, starting with:
- who is the map's audience, and what is the map's
purpose? Does it have a theme?
- how large is the mapped area? Small as a town, or the whole planet?
- what is the appropriate scaling factor?
- which sources of data are available?
- which is the geodetic model? Spherical of elliptical? If the latter,
which datum is the best?
- depending on the map's audience, theme and purpose, which
properties must be preserved,
emphasized, or maybe hidden?
- which projection is most appropriate? Does it have details
to tune, like standard parallels, or a central meridian?
- would changing the aspect, for instance making the map
improve the result?
- are further modifications, like interrupting the map, helpful? How about
cropping, condensing, or recentering?
Not every choice is completely independent. For example:
- the mapped area and scale are roughly inversely related
- choropleth maps (which represent relationships as colored or patterned areas) and
other thematic maps presenting densities should use equal-area projections
- a few projections are only developed for ellipsoidal models, while many are
only available for spherical data
- some projections have little meaning, or are difficult to compute, in aspects
other than the normal
Therefore, the study of map projections is only a small, but very important,
part of the cartographic job.
Copyright © 2012 Carlos A. Furuti
| ||www.progonos.com/furuti October 29, 2012|