Similarity matrices take similar data sets and put them in a matrix with eachother to illustrate the similarities, which become increasingly evident in matrix form. It has many biological applications, as seen here with this amino acid table.
Found - http://mendel.ethz.ch:8080/Server/ServerBooklet/_17545_tabular891.gif
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!