I am trying to apply a Gaussian decay value to a set of distances measured in meters using the field calculator in QGIS.

My distances range from circa 50 to 12,000 meters. I am using the following equation which works but I am confused by the sigma value. Mainly it's purpose and how you find a suitable value for your data set so it is meaningful. For my range I need a sigma value into the 1000s before a number other than zero is returned.

exp(-("Distance" ** 2) / (2 * ([Sigma]**2)))

My understanding of maths is fairly basic so if this could be explained in Layman's term that would be great.

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