Graphic Map Load Measuring Tool (GMLMT) is available for download under the licence CC BY-SA. The tool is a Python script for open-source graphic editor GIMP. After putting the file into the extensions folder of GIMP, you can find the tool in the menu Filters → Edge-Detect.
GMLMT is suitable for all raster representations of a map in RGB (RGBA) colour space. To provide comparable results, the original map dimensions and 100 DPI image resolution are recommended. GMLMT measures graphic map load of the whole map or of a user-selected extent defined by GIMP built-in tools.