You cannot take the log of a negative number or 0. The number must be positive and non-zero. This is not Surfer's rule, but a mathematical one. The log of (X) becomes asymptotic as X approaches 0.

If you already have a contour map from a grid file containing some negative or 0 values and you're trying to set the Level method to Logarithmic, then you will get an error that the minimum contour level must be greater than 0.0. Click OK to dismiss the error and then change the Minimum contour value to be a non-zero positive number. At that time, you will be able to change the Level method to Logarithmic.

If you already have another grid-based map (like a color relief map) from a grid file containing some negative or 0 values and you're trying to use logarithmic scaling for your colormap, then you will get an error that logarithmic scaling requires positive data. Click OK to dismiss the error and then change the Min and/or Max data value(s) for the colormap so that they are both non-zero positive numbers.

Updated December 19, 2021