I think the HEATMAP and HEATMAPPARMS statements provide for a uniform grid of X-Y values. However, you might look into using a bubble plot instead of a heat map. The bubble plot is designed to have the marker sizes that vary according to the value of some response. If you use a bubble plot, you might have to bin the data yourself. For examples, see "counting observations in two-dimensional bins" and "Designing a quantile bin plot."  For bubble plot basics, see "Getting started with a bubble plot." ... View more