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I have a point shapefile concerning rainfall for the whole country. The points represent the annual rainfall in mm and range from 675-3562. I have approximately 800 points.

I am attempting to use Ordinary Kriging in QGIS to create a smooth raster surface.

I have used the Saga GIS ordinary kriging tool whith the following paramaters altered from the default:

        Block Size: 1000
        Cellsize: 1000

This has successfully created a smooth surface, however the range in values does not match my point data. The Ordinary kriging output has values ranging from 798-2273 - Why is this?

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Kriging is an interpolation method, and only if your data points are colocated with your estimated points (the output grid, usually) will you get back mean estimates with the same range as the data.

If you do the same kriging on an even finer grid, you might get a more expanded range of kriging means since there's probably a grid point closer to your data.

  • Thank you for your reply. Is there a way to colocate the estimated points? I have examined by output grid and the correct values (675-3562) seem to be present in my raster at the appropriate locations. However, the legend and the max and min present on the histogram tab match the incorrect values (798-2273). – Will.S89 Oct 6 '18 at 18:58
  • how are you getting the max/min values? Sometimes because rasters can be large you will only see statistics based on a sample of your raster. Is that happening? Hard to tell without your data or some test data... – Spacedman Oct 7 '18 at 10:00
  • If I look in the attributes table of the point data, and order the values the lowest is 675 and the highest is 3562. Once I create the kriged surface the lowest value in the legend and histogram for the kriged surface is 798 and the highest value is 2273. You are probably correct in saying that I am only seeing sample values. Thank you for your help. – Will.S89 Oct 9 '18 at 8:50

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