Values of a physiologic parameter at respective measured points in a heart are obtained. A 3-dimensional model of the heart is constructed, which includes first spatial elements that include the measured points and second spatial elements that do not include the measured points. The values of the parameter in the second spatial elements are interpolated and regional densities of the measured points in the model determined. The values of the parameter at the first spatial elements and the second spatial elements are displayed on a functional map of the heart, and a graphical characteristic of the map is modified responsively to the regional densities.