176 sYMBOLizaTiOn
While this isn’t
a strong correlation, this palette has become conventional. There
are variations on this sequence, however. Some commercial firms use white for the
highest elevations, giving the impression of snow-capped mountains, and some have
used purple, presumably based on the appearance of mountains seen in the distance.
Frequently, relief shading is added to the hypsometric tints.
LegenDs FOR isaRiTHMiC MaPs
If the isarithmic interval is even, lines are identified on the map, and no layer tints
are used, a simple statement of isarithmic interval can be enough, as in Figure 8.25;
however, if layer tints are used, a legend showing the value scale is required. Because
it is the lines that are important, not the shading, the ramp (lightness scale) is best
shown by adjoining tones separated by lines and the line value marked on the line,
as in Figure 8.25. It is not appropriate to show categories such as 10–20, 21–30, as
on a choropleth map, because that gives an incorrect impression that the shades and
categories are most important rather than the values. The tints are there simply to
aid the reader in finding and interpreting the isarithms. Separate boxes should not be
used in any case.
choosIng symBol tyPes
Whether one chooses quantitative points, choropleths, isarithms, or qualitative point,
line or area symbols depends on several factors that were described in Chapter 7.
These factors are the nature of the phenomena, the form of the data, the appropriate
visual
variables, and the tools available. These factors are summarized in Table 8.4.
