Gimp script: Selection area finder

[isomage]

For a test, I computed the area of Texas using this image.

The image is 750 x 733 pixels. According to its scale, 96 pixels = 100 miles.

Selecting Texas and running the script gave 47.2%. The selected area was then (100 / 96)^2 * 750 * 733 * 0.472 = 281556 square miles.

Wikipedia says that the area of Texas is 268820 square miles. If the map and its scale are perfectly accurate, then we've overestimated by a little less than 5%.

That's not too bad an estimate, considering that the map may not be perfectly accurate; a scale of 98.2478 pixels per 100 miles, instead of 96, would have given a correct result -- a mere two pixels of difference.