Choropleth Map
A choropleth map uses different gradients of color that corresponds to a certain quantity or average to represent specific areas on a map. These maps are most commonly used to display population density in certain areas. The map on the right displays the population in the counties of Georgia in 2000.
Dot Density Map
A dot density map is also another kind of thematic map used to show population. On a dot density map, each dot represents a specific number. The map on the right displays the Hispanic population in the United States. The areas with the most dots have the largest Hispanic populations.
Proportional Symbol Map
On a proportional symbol map, the area of the symbol (normally circles like below) corresponds to whatever is being measured. The map on the right displays the total murders per state in 2009. The states with the larger dots have a higher total of murders than those with smaller dot. The legend in the lower right corner denotes the number of murders for each dot size.
Isopleth Map
An isopleth map uses contour lines to display variation in value such as, elevation, depth, and inches of rainfall. There are several different types of isopleth maps. A bathymetric map displays the variation in depth of bodies of water, and a topographic also uses contour lines to show variation in elevation. The map on the right is a bathymetric map of the Gulf of Mexico. The lightest areas on the map represent the most shallow parts of the Gulf, while the darkest areas indicate the deepest points.
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