Data considerations for Heatmap

The data must include at least two columns of numeric or text data
The columns must have the same number of rows. You cannot include any columns with date/time data.
The sample size should be large
Although there are no formal guidelines for the amount of data needed for a heatmap, larger samples more clearly indicate patterns in the data.
The sample data should be selected randomly
In statistics, random samples are used to make generalizations, or inferences, about a population. If your data were not collected randomly, your results may not represent the population.