Cartographic Representation - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 204

Quantile. The quantile classification determines classes to ensure that
each class has approximately the same number of features. This classification
produces results that best show the diversity of a geographic property and
can aid in determining relationships, or can lead to questions about possible
relationships.
Natural Break (Jenks). Also known as the “Jenks classification” after the
cartographer who developed it, natural breaks use an algorithm to deter-
mine where class boundaries should be placed in the total range. The class
boundaries should maximize differences and keep similar clusters together.
This classification is very valuable for visualizing GI in an insightful manner.
Standard Deviation. The standard deviation classification is different
from the other three. It shows graphically how much a geographic unit's
property varies from the mean. This is useful for cartographically represent-
ing differences in geographic properties from an average value rather than
showing exact values.
Symbolization
Things and events require additional abstraction for certain mapping and
visualization purposes. The symbols for elements from the geographic rep-
resentation can be varied in terms of size, shape, value, texture, orientation,
and hue. These symbols are used to represent location, direction, distance,
movement, function, process, and correlation in an infinite number of ways.
The design of cartographic materials draws on long traditions and scientific
study of these symbols and their role in cartographic representation and
communication.
Pragmatically, size, shape, and hue are perhaps the most significant. Size
is important because humans will instinctively understand that a larger dot
on a map of the world means a larger city than a smaller dot or that a large
runway symbol indicates a large airport. Size shows quantitative differences.
Shape provides clues about qualitative differences. Shape is also important
because it gives us an orientation to the actual shape on the ground of the
feature and because it helps us to understand geographic relationships. Hue,
which refers to what most people refer to commonly as “color,” is so signifi-
cant that it requires its own section.
Color, Otherwise Known as Hue
A key component of most maps is color. Humans have an astonishingly
broad perception of color, but a surprising number of people face limits in
distinguishing color (color-blind people and others with visual or perceptual
impairments) and many people will not agree on the name of specific colors.
Color is very important for maps and visualization. A good application of
color will greatly help with communication.
The first principle to remember is that the use of color should be dis-