The rank report is multi dimensional heat-map which has been designed with search rank performance reports in mind.
Here, 3 dimensions and one metric have been selected in the report builder.
When setting up the report as a rank report, rank must be the first selected dimension, followed by search term which appears along the top as columns, with the domain name returned as the 3rd dimension which is the value within the table.
The main metric, searches is totalled below the search term.
If your report is not a rank report, your data will act as an alternative form of a heat-map, the difference being that you can map 3+ dimensions (normal heat-map only works with 2).
The third or final dimension will be broken down within the heat-map itself. You can choose more than 3 dimensions but the final dimension chosen i the report builder will always be broken down within the heat-map.
Here we can see clicks broken down by market (left) and publisher (top) and then by device displayed within the heat-map.
You can also choose multiple metrics which you will be able to toggle between at the top: