**nominal data:** showing differences
in kind

**ordinal data:** showing relative
differences in quantities as well as kind

**interval data: **is information
that can be arranged using a standard scale along which operations of addition
and subtraction have meaning. Temperature is an example of an interval measure.

**ratio data: **

is information that, like interval data, can be arranged along a scale but, in addition, the scale begins at a non-arbitrary zero point. At the zero point, no features are present. The operations of multiplication and division can be employed with ratio data to consider proportions and magnitudes. Elevation above sea level, precipitation, and population are all examples of ratio data.

Graphics compiled from the University of Texas Cartographic Communication website.

See The Cartographer's Palette: The Semiotics of Cartography