Representing spatio-temporal phenomena through maps

Sara I. Fabrikant

Long version:

“Maps are products of art clarified by science” (Eckert, 1921/25). Maps have been used for at least 5000 years to communicate about tangible and intangible environmental phenomena. Cartographers distinguish two broad categories of maps: all-purpose (reference) maps and thematic maps. Reference maps serve as visual archives of spatial data. A reference map of Santa Barbara, CA depicted in Figure 1 gives answer to the spatio-temporal questions “where?, when? and what?” is happening in the environment?

Figure 1: Reference map of Santa Barbara, CA (© yahoo!maps.com)

Thematic maps are a more recent phenomenon. They emerged alongside the rise of statistical graphics in the 17^th century (Tufte, 1983). Statistical maps typically include a base map for spatial reference and a statistical overlay for depicting a spatial pattern of an attribute. Thematic maps tell a story; they are graphic essays about a specific event in the environment . The thematic map shown in Figure 2 depicts the distribution of Latinos in Santa Barbara in 2000. This map not only answers the spatio-temporal questions “who lives where, and when?”, but may also suggest potential answers to the scientific question “why do they live there?”.

Figure 2: Thematic map of Latinos living in Santa Barbara, CA in 2000.

Geographers use thematic maps as visual tools to explore spatio-temporal processes. More recently interactive and dynamic graphic computer displays allow cartographers to utilize thematic map as an interactive interface to a real-time data exploration system (Slocum et al., 2003).

This paper reviews cartographic principles, specifically focusing on population maps. The nature of geographic phenomena and derived spatial data for thematic mapping will be discussed, including symbol types and their visual dimensions. Map examples will include the popular choropleth map, where attribute data are mapped into data independent enumeration units, as well as less common depiction methods such as value-by-area cartograms.

Work Cited

Eckert, M. (1921/25). Die Kartenwissenschaft, DeGruyter, Berlin, Germany.

Slocum, T. A., McMaster, R. B., Kessler, F. C., and Howard, H. H. (2003). Thematic Cartography & Geographic Visualization, 2nd Edition, Prentice Hall, Upper Saddle River, NJ.

Tufte, E. (1983). The Visual Display of Quantitative Information, Graphics Press, Cheshire, Connecticut.