Any type of information on a map (or in a table, a list, a survey,
etc.) can be described in terms of how pieces of the information can be
related to each other. Examples of mapped information include land-use
classes, road classes, city populations, and county areas.
We can think of these types of information as either categorical (or
qualitative) or numerical (or quantitative). Categorical information can
only be described qualitatively, whereas items of numerical information
can be compared quantitatively. That is, numerical information is on a
real scale, such as distance (e.g., kilometers), area (e.g., hectares),
or temperature (e.g., Celsius).
Example of categorical information:Land-Use categories of :1= forest, 2 = grassland, 3 = urban;We cannot say that based on the classes, 1 + 2 = 3 !We can only use the numbering to describe the items qualitatively.Example of Numerical information, city populations:Springfield = 100, Harmony = 200, Centerville = 300;We can say that Centerville has as many people as Springfield and Harmony.