I'm trying to figure how many waters surface level does this map cover
So how do i count the % water surface cover over land.
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1$\begingroup$ Hi CakeMinh, I don't think this is a good fit for our site. I recommend asking this at Software Recommendations, because I'm sure there is some application out there that can calculate the percentage of red pixels in your image. $\endgroup$– JoachimCommented Jan 21, 2022 at 8:10
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$\begingroup$ I means the blue part, the red thingy is a different stuff but okay $\endgroup$– CakeMinhCommented Jan 21, 2022 at 9:08
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2$\begingroup$ While I feel this could be answered better elsewhere, I think it could still be considered a worldbuilding question. $\endgroup$– DWKrausCommented Jan 21, 2022 at 15:39
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$\begingroup$ Based only on a 2d-map, without any data about the shape of this planet, there's little to say about the percentage of water surface, no software can provide that without more input. vtc for missing info and yes.. this is off topic too. Power Users, maybe ? $\endgroup$– GoodiesCommented Jan 21, 2022 at 17:05
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1$\begingroup$ Would you mind editing your question to clarify it and add details about the object/planet this map depicts? As it is now it is really hard to understand what are you asking. I would also suggest adding the legend to the map to avoid confusion. $\endgroup$– OtkinCommented Jan 21, 2022 at 19:52
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I just opened your image in GIMP and selected all the blue pixels including two small lakes (if I understand your task correctly). Then I used the Colours → Info → Histogram menu to see, how many pixels were selected, and it was 4945535. The total number of pixels is 2976 × 2262 = 6731712 (the same number I see with Histogram). So, the water % is 4945535 / 6731712 ≈ 0.7347, which is 73.47%.
Maybe, moderators want to move this question to Software Recommendations, but I still hope my answer was useful. If you mean to calculate the red pixels, not blue ones, you can use the same algorithm.
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1$\begingroup$ If the map is in any other than cylindrical equal-area projection the result will be wildly inaccurate. They should first load the map in a software tool such as NASA's G.Projector and export it as cylindrical equal-area... $\endgroup$– AlexPCommented Jan 21, 2022 at 8:57
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$\begingroup$ @AlexP would Earth not be hard-coded in that Nasa software ? the opening says nothing about the shape of the planet. This world may as well be banana-shaped.. or an extremely flattened spheroid.. Nasa won't provide you with data about the transformation ! $\endgroup$– GoodiesCommented Jan 21, 2022 at 17:02
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$\begingroup$ @Goodies: The only hard coded assumption in G.Projector is that the world is spherical. You can load any equirectangular map you want. The software is agnostic about the size of the world. (And it really assumes that the world is spherical. There is no correction for the small oblateness of real-world planets. But then, at the scales where such maps are drawn this doesn't really count for much.) $\endgroup$– AlexPCommented Jan 21, 2022 at 18:26
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$\begingroup$ Curious: did you import the map as a rectangle or as a globe? $\endgroup$ Commented Jan 21, 2022 at 19:13
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$\begingroup$ Since there were no instructions in the question, I assumed the world is giant flat rectangle standing on the backs of four flying giraffes in the way when each of their heads looks like the sun in the ice cream glass on each side of that rectangle. Hope it is the same the author assumed. Otherwise, my answer will be wrong in case of other planet form. Thanks for comments! $\endgroup$– NecrosCommented Jan 24, 2022 at 21:17