Here are some examples of dot density maps.
I found this one at http://www-personal.umich.edu/~copyrght/image/solstice/sum05/dotdensitymap/overviewI.html
Here are some examples of dot density maps.
I found this one at http://www-personal.umich.edu/~copyrght/image/solstice/sum05/dotdensitymap/overviewI.html
I found this one at http://gsc.nrcan.gc.ca/mindep/metallogeny/vms/bathurst/index_e.php
I found this one at http://geography.asu.edu/gallery/vca/index.php