Heat maps with multiple index columns display a rectangle hierarchy. The number of levels of the hierarchy is the number of columns from the visualized data table that are specified as index columns.

In such a heat map, there is a rectangle at level n for each unique sequence of values from the first n index columns, for every level between 1 and the number of index columns, inclusive.

For a given such sequence of n index values, the area of the corresponding rectangle is proportional to the result of aggregating the values in the size-data column in those rows whose first n index columns contain the values in the sequence. You specify the type of aggregation to use (sum, count, average, min, or max) with the sizeValueGroupType property.

In addition, for a given such sequence of n index values, the color of the corresponding rectangle is determined by the result of aggregating the values in the color-data column in those rows whose first n index columns contain the values in the sequence. You specify the type of aggregation to use (sum, count, average, min, or max) with the colorValueGroupType property.