Final answer:
A choropleth map is used to represent statistical data across geographical areas by shading or patterning regions in proportion to the variable of interest, like population density. It is particularly useful for visualizing spatial patterns and trends within a region. Option number c is correct.
Step-by-step explanation:
A choropleth map is a type of thematic map in which areas are shaded or patterned in proportion to the measurement of the statistical variable being displayed on the map, such as population density or per-capita income. The choice 'c) intensity of color reflect intensity of phenomena being mapped' correctly defines a choropleth map. These maps assist in visualizing how a particular variable changes across a geographic area, showing the level of variability within a region.
Choropleth maps can highlight spatial patterns such as clustering. An example of clustering might be neighboring states with similar data values, indicating a regional trend. Spatial autocorrelation, like Moran's I, is used to measure the degree of clustering on a choropleth map, thus giving geographers tools to analyze and interpret spatial data effectively.
Importantly, while choropleth maps are useful for showing general trends and patterns, they may oversimplify complex data. As observed in political voting patterns, a state-level choropleth map might not accurately reflect the nuanced voting behaviors that occur within states, particularly in urban versus rural areas. These nuances can sometimes result in the ecological fallacy, where assumptions about individual level data are incorrectly inferred from aggregated data.