Alpha Mask by Density
The alpha mask by density feature applies an alpha mask according to the contributing data's density, in effect a Kernel Density Estimation (KDE). It is helpful when visualizing an averaged heat map. With an alpha mask by density you can highlight the origins with a high number of contributors.
This concept is comparable to the prediction standard error surface in geostatistics.
The alpha value is used together with the averaged value in a bivariate color scale, where calculated data points become more transparent the fewer of them and the farther away they are from their input samples.
The image below shows a heat map with and without an applied density mask: