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My query is related to area calculation in mountainous areas. There is a simple method in QGIS to find the area of any polygon, like we need to project shapefile in the required projection system and then just write $area in attribute, to calculate the area. But when it comes to mountainous areas this method is not valid, according to my knowledge. 

Is there any method or analysis to correctly find the area in such regions that are highly mountainous as well have low profile areas? 

Below I am attaching the screenshot of the polygon and calculated the area using the aforementioned method which is 1100 hectares, which is not correct. As it has high ridges and a mountainous regionsteep slope.

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    You mean the actual "sloped" area? it is possible, but you would need some kind of 3D model to compute it.
    – RafDouglas C. Tommasi
    Commented Oct 6, 2022 at 7:51
  • You can download SRTM tiles from here: dwtkns.com/srtm30m
    – RafDouglas C. Tommasi
    Commented Oct 6, 2022 at 7:55
  • No, it is not the actual slope area of the region. If download dem then how i am going to find the area of such region?
    – Shumaill
    Commented Oct 6, 2022 at 8:04
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    Is the height of the hill of the same order of magnitude as the width of the valley? if not then the change in area is negligable
    – Ian Turton
    Commented Oct 6, 2022 at 8:47
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    Do you mean the surface area like in this article researchgate.net/publication/…?
    – user30184
    Commented Oct 6, 2022 at 8:52

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For my use, I have this solution:

First I convert my DTM with the tool from SAGA called "Real surface area". After that, I have a raster with the real surface for each pixels, on band 1.

Than I simply use "zonal statistics" with my polygones layer, to get the 'sum' of band 1... and that's it!

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