A Correlation Matrix is a graph view of the correlation between two numeric values.  This example is showing us the correlation between different criminal justice aspects of other countries.

correlation map

Similarity Matrix

A Similarity Matrix is a matirix of scores that shows the comon characteristics between two data points.  This comes in useful when comparing or contrasting similar sets of data on a graph.  The example we are shown here is comparing the output of multiple machines to see what they have incomon and what their differences are.

Similarity Matrix