Multivariate Mapping 183
Radar graphs, snowflakes, stars, and Polygonal glyphs
Radar graphs, also called
star graphs or
spider graphs, are graphs used for compari-
sons of quantities. Each ray represents a different category and tick marks on the rays
indicate measurements of amounts (Figure 9.7). Unlike pie charts, the length of the
ray, not the size of the wedge, is important.
Ray glyphs simply show the radii, with
each ray drawn proportional to the attribute without tick marks.
Snowflakes are cre-
ated by joining the end points of rays on radar graphs and eliminating the tick marks;
polygonal glyphs join the end points of the rays to create irregular polygons, but the
rays are eliminated. It is important to remember that for all of these graphs, it is the
length
of the rays that is important, not the area or size of the segments.
Climate graphs
Line and bar graphs called
climographs representing climate information of tempera-
ture and rainfall are often used on maps to show the nature of the temperature and
rainfall regime for a place (Figure 9.8). These may be included as illustrations sur-
rounding the map proper as exemplars of climate types or miniature versions may be
placed at points on the map to show climate at specific places.
Any of these graphs may be combined with other symbols, such as choropleths
or isarithms, to add additional variables. However, there is danger of creating a clut-
tered, hard-to-read map if too many variables and symbols are used. The purpose of
these point graphs is to compare variables and make the information easy to grasp; too
much information defeats this purpose. Multiple maps might be more user-friendly.
