Heat map uses 1 or 2 measures against 1 or more Dimensions. Marks on a chart are represented as colors on Heat map visualization. Marks are heated up by values or based on density of records, more the intensity of colors more will be the values of the records. These visualizations can be shown in matrix/crosstab format in a highlighted tables. But other than the tables, geographical view and customized image like webpage can also be used for heat map visualization.
Below are the requirements to visualize heat map in tableau under ‘Show me’ option:
1. Try 1 or more dimension and 1 or 2 measures for heat maps
2. Try 1 or more dimension and 1 measure for highlight tables
The key difference between them is that for in highlight tables you can color the marks by 1 measure only at a time. But in heat map you can color the marks by 1 measure and for resizing you can use 2nd measure. So this additional encoding will help you take more insights from the visualization at a time.
You can learn more visualizations in tableau for that you can check tableau tutorial