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I've applied Mathematica to the problem of estimating the area of an estuary, but when I got the results I wasn't able to understand in which unit of area it was given. My approach is the following:

Here is the image of the shape of the estuary:

The shape of estury that I've used,

The horizontal line in the lower right side represents the scale, namely its length represents 1 kilometer.

Using the routine: 

img = Binarize@
Import["C:\\Users\\Klën\\Documents\\Wayner - USP\\Rio Doce\\No \
estuário\\cont2.jpg"]~Erosion~1;
(m = MorphologicalComponents[img]) // Colorize

I've got:

Image binarized and colored.

And, applying the following code I've got the total area of pink region

in[63] = 2 /. ComponentMeasurements[{m, img}, "Area"]
out[64]= 461259.

But I really don't know in wich units the result is given, I would like to show the results in $km^{2}$, how could I do that?

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    $\begingroup$ Use the "get coordinates" tool to find out how many pixels wide the scale is, then divide your area by the square of that. $\endgroup$
    – C. E. ♦
    Commented Nov 29, 2015 at 4:16
  • $\begingroup$ Thank you @Pickett, then Is the unit always given in pixels? $\endgroup$
    – Herr Schrödinger
    Commented Nov 29, 2015 at 4:22
  • 2
    $\begingroup$ For operations on 2D images I can't think of any other unit. $\endgroup$
    – C. E. ♦
    Commented Nov 29, 2015 at 5:14

1 Answer 1

Reset to default
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linecount = 
  3 /. (Binarize@Import["https://i.sstatic.net/Wmeps.jpg"] // 
       ColorNegate // Thinning // 
     ComponentMeasurements[#, "PerimeterCount"] &);
areacount = 
  2 /. ComponentMeasurements[MorphologicalComponents[img], "Count"];
areacount/linecount^2 // N

9.70249

The area is $9.70249 km^2$ I think.

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