Unclassified Choropleth

This is a map of the population trends in France in 1836. It is unclassified because it is created using a gray scale and has as many units as intervals.

http://go.owu.edu/~jbkrygie/krygier_html/geog_353/geog_353_lo/geog_353_lo08_gr/choro_1836.jpg