Image overlay with opacity varied based on numerical data values

Methods and means are disclosed for superimposing data on an image using a variable opacity based upon variations in the numerical values of the data to be superimposed; this allows for representing data most prominently where it the values are higher, while providing a clear view of the surrounding features. In one aspect, a colour (color) scale is determined to represent numerical data values. Alternatively, there is a means for obtaining data, means for obtaining an overlay image and means for overlaying the data on the image. Further, the overlay is computer generated in one aspect. The underlying image may be a map or other cartographical display, and the overlaid data information may be power density (e.g. from a transmitter), probability, location, acoustic, weather, particle density, energy / power distribution or medical image data. Opacity scaling may use non linear logarithmic, exponential, polynomial, discrete steps, Fibonacci, factorial or sinusoidal functions.