The first map is an example of a dot density map.  A dot density, or dot distribution map is a map that uses a dot symbol to express a feature or phenomenon. 

The following is an Isopleth Maps. This type of map is ideal for showing gradual change over space and avoids the abrupt changes which boundary lines produce on choropleth maps. Temperature, for example, is a phenomenon that should be mapped using isoplething, since temperature exists at every point (is continuous), yet does not change abruptly at any point (like population density may do as you cross into another census zone).

The third one is an example of choropleth map. 

The last type of map is a proportional symbol map.