Proportional Symbol Map and Isopleth Map

A proportional symbol map is used to describes proportions in relation to a set of data.The larger the dot or symbol, the higher the proportion. For instance, the map below shows the porportion of Walmart stores in each state. Source: http://personal.frostburg.edu/sbriggs0/maps.htm

An isoleth map uses shaded linesto define regions of data. For example, an area between shaded lines would indicate how much rain had fallen in the area in the past year. The image above demonstrates average temperatures in different regions. However, the above image is easily confused with a choropleth map, due to the coloring of the regions.

Source : http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/clravt.gif