Isohyets

http://droughtsheatwaves.suite101.com/article.cfm/australian_drought_a_natural_cycle

An isohyet is a line joining points of equal precipitation on a map. A map with isohyets is called an isohyetal map.

This map is from the Commonwealth of Australia and depicts the median rainfall from January to March and is based on climatology data between 1900 to 1999.