The scale represents the size of the heatmap to generate. 

A scale of 1 means the heatmap will be the same resolution as the map overlay and has no loss of detail. A scale of 0.5 means the heatmap would be 1/2 the size, and a scale of 2 would be double the size. When a heatmap is displayed on top of a map overlay image it is stretched automatically to fit the actual overlay image.

The larger the heatmap the longer it takes to process the image and the larger the file or database storage is required.

<b>Recommendation:</b> 0.5 (with a brush size of 'medium')