3 scales of measurement

As seen before, the Geographic information richness content is partly expressed through the scale of measurement used to describe properties of each phenomenon:

• Nominal scale: thematic properties are coded as mutually exclusive categories. Properties can be identified and differentiated through numerical coding.
• Ordinal scale: properties can be ranked in a hierarchy of states (classes). As with the nominal scale, a quantitative analysis of ordinal measurements is restricted primarily to counting observations in the various states. However, we can also consider the manner in which different ordinal classes succeed one another. This is done, for example, by determining if states tend to be followed an unusual number of times by greater or lesser states on the ordinal scale. Ordinal level is rarely used for the description of properties in the geometric dimension, except for some topological properties. Time dimension is often expressed by sequence of ranked levels (periods of time).
• Cardinal scale: it is so named because of the length of successive intervals is a constant and is generally considered as continuous. Digits and the sign of numbers as well as their unit of measurement fully describe the rich content of properties. Cardinal level is mostly used to describe properties in the geometric dimension (coordinates, geometric properties, proximity, …). Time can be expressed at this level as a continuous scale (time continuous function).

Remember that the level of measurement strongly influences the potential use of descriptors and operators applied to process numerical information.