I having been creating interpolation surface maps, from set water quality sample points, and have been using the Spatial analysis tool>interpolation>IWD to get my interpolated surfaces. Macrophyte (water quality samples) data is recorded in ug/m2. I have a set of categories I use in symbology tab to show the various measured categories (as seen in my images below). However, some sample points only show low levels of macrophytes at specific sampling sites, but when I use the IWD interpolation and the set categories it has the whole area showing that it is a low range. I am not too sure if this can be corrected by changing my categories or if there is a better interpolation method to use.
Any suggestion or advice would be great.