Unclassed choropleth maps run on the same basis as other choropleth maps, but lack the the data classification of classed maps. They have not been widely accepted because of the fact that in turning away from the standardization of classed choropleth maps, they have isolated themselves in a less understood faction of mapping.
Found - www.sfu.ca
This blog is a map catalog in which I am displaying fifty different types of maps and a tid-bit of information that looks into the purpose of the map!