To utilize them in a GIS you need to organize them in various ways. To help think this through you can use the following chart. David Sinton proposed this framework that differentiates between space, time, and attribute and fixed, controlled, measured. Geographically this is called a 'surface' , mathematically a 'field', even if the value is a category. Measured A vector map of soil types or hospital costs by state would have space measured, time fixed, and attribute controlled.
Time is fixed.
Geographic Information can also be represented in other forms. A well known form of temporal GI are strip charts. A strip chart of stream heights taken at a pier would have space fixed, time controlled and attribute measured. This can be used to rank categories, or to assign interval or ratio values to a category. Such a step has to be justified by some impression that the value applies uniformly to the whole class.