HeatMap is another data visualization tool which has been widely used for examining correlation between data rows or columns.
All three pictures above show correlations between features (column data values) in regards to ‘how much they are co-related to each other’. For instance, if their correlation is very high (i.e., very similar) then the color of the each small square dot will be 100% black in first BLACK-WHITE map, and 100% red in second RED_GREEN and third RED_BLUE maps. The data set used here is one of the Alzheimer Disease data sets that I utilized for collaboration work between CSJL solutions and my research team in Edith Cowan University.
This is one way of showing or revealing relationships of data points on the given data set. Obviously, it is much easier to pick up some facts by looking at these pictures, rather than staring at a bunch of high precision numbers.