I have to save to .png file with part of map from app.

I've got information about PPI, easting/northing, print resolution, map scale and map coordinate system and using this information I have to calculate a size of pixel (in meters) given information about curvature of the earth. I have to know how many meters on earth is representing by one pixel on my picture.

I was trying to find any pattern for that but without success.

Anybody here know how can I calculate that?

  • 1
    If you have the corner coordinates of the image, can't you just e.g. get the vertical difference via subtraction, then divide by the number of rows in the image to get the vertical pixel resolution?
    – Jon
    Commented Sep 28, 2020 at 14:27

2 Answers 2


Gdalinfo or raster information in processing toolbox will give you that information if the image is georeferenced. You can also find the information in the layer properties.

If you don’t have QGIS, you can use Gdal info from the command prompt.


If not (max x coordinates -x min coordinates) / x pixels


A simple method to measure pixel length is to zoom the image of the map until you can identify each pixel cell, then using the ruler you can get the size of it. For example I'm using Qgis, but you must georeference the map in order to get the true length.

enter image description here

  • I have to calculate that by application code because I'll need that value to another calculations, for example to calculate size of scale bar length. So I need to have a pattern for that.
    – Presto
    Commented Sep 28, 2020 at 14:00

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