Global Mapper v25.0

Compute % of Polygon Area falling within an overlaping Polygon

I have hundreds of polygons in Shapefile format (source polys).  I need to compute, for each source polygon the area found within a second confining polygon.  The source polys will exist both inside and outside of the confining poly.

I have no idea where to go inside of GM V21 to set up this type of computation.
Also is there a way to automate this function and write a report of the results into a spreadsheet?


  • Just an idea. Use the confining polygon as the export bounds and export the source polygons out; essentially cropping them to your confining boundary. Then import back in and compare the areas against the original polygons.
    1. Select the confining polygon
    2. Right-click on source polygons layer:  Layer > Export > Shapefile
    3. Choose Export Areas
    4. Go to Export Bounds tab
    5. Choose Crop to Selected Area Feature(s)
    6. Import this new shapefile
    7. Turn off all layers except the source polygons
    8. Search > Search By Attributes, Name and Description
    9. In the Attribute Editor click on the Save to CSV button
    10. Export the data
    11. Repeat for the cropped source polygons
    12. Use Excel to compute the percentage between the original and cropped ENCLOSED_AREA values. Any feature that are absent from the side-by-side comparison have a percentage of 0.