Since data in a heat map is aggregated, the value shown in a node might not be the same as the value passed down to a drill down display. For example, suppose your heat map is attached to a table where the index column is Plant and the size column is Units Completed. If you have two rows where the Plant is San Francisco, then the node size is based on the total of the Units Completed values for both rows. However when you drill down, the drill down value for Units Completed will be the value in the first row in the table where the Plant is San Francisco.