Dot Density Map

I had trouble finding dot density maps...Google search didn't get me very far.

I found this dot density map at the USDA web site at the following link:

http://www.nass.usda.gov/research/atlas02/atlas-livestock.html

I thought it was interesting because it shows two colors of dots to depict the changes in the number of cows. Blue for increase and Red for decrease. The quality is not the best...bad figure-ground because it is too washed out. I had to save the PDF and convert to JPG.