1.
A chloropleth map is a thematic map on which different areas are color-coded, shaded, or patterned in proportion to the measurement of the statistical variable being displayed on the map. In this example, the variable would be population change. This example indicates that Nevada has had the biggest population change between 1990 and 2000.
2.
A dot density map is a map that uses a dot or symbol to indicated the presence of a feature or phenomenon within certain boundaries. It does not matter where the dot/symbol goes in the boundaried area. There is always a numerical value associated with the dot. This map indicates that nonmetro poor are present in bigger numbers in the eastern states.
3.
A proportional symbol map is a map in which the areas of symbols are varied in proportion to the value of an attribute. Each symbol varies in size according to its value. In this example, each disc indicated how many Walmarts are in that specific state.
4.
An isopleth map is a map that uses lines with different values to delineate boundaries. The map consists of contour lines that depict a variable which must be calculated from data collected over an area. Isopleth maps are used in weather and to indicate how steep certain terrains are.
Severe weather link (abc Action News):
http://abclocal.go.com/wpvi/story?section=news/local&id=8787041
