Set marker size equal to GPS accuracy with variable opacity?

Question

I have an exported collection of iNaturalist observations which have latitude and longitude values, but also report the GPS accuracy in meters. This data is in the form of a csv file.

The accuracy varies from observation-to-observation, which I would like visualized by the marker size. Because there are some areas where the markers have poor accuracy, I don't want those points to mask the other nearby observations that may be more precise. To tackle this I would like to set opacity of each point to be a decreasing function of the accuracy. One approach might be to take 1 - S(d) where S(d) is a s-shaped curve over the accuracy score d.

How can I plot the position of observations (lat/long) such that the marker size is equal to the accuracy, and have the opacity decay with the (in)accuracy?

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• I am new to QGIS, so many of the available objects are unknown to me. But I am experienced with Python, so a scripting solution is fine.

Answer 1

You can set an attribute based expression to do what you are trying to accomplish. By clicking on the highlighted red rectangle and "Edit..." and inserting the following expression:

100 - scale_linear("ACCURACY", minimum("ACCURACY"), maximum("ACCURACY"), 20, 100)

"ACCURACY" being your field with your "GPS accuracy in meters" that I understood as being an inaccuracy field