Isohyets

http://traveloutbackaustralia.com/start-here/outback-climate-and-weather.html

Isohyets are lines that group regions in an area that have similar amounts of rainfall during that period of time.  The image above breaks down the entire country of Australia into colored sections depending on the amount of rainfall each region received that year.  The darker the shade of green indicates regions across Australia that experienced the heaviest amount of rainfall, mostly located on the northern and eastern coastline.  As the green shades become lighter on the map means there is a decrease in the amount of rainfall.  The white areas on the map show the least amount of rain fall which is the desert region in the middle of Australia.