We have produced an interpolated map using the IDW tool from the Spatial Analyst extension, with a cell size of 1,000 meters and a fixed distance of 4,000 meters. Other parameters are defaulted. The attached illustration shows a detail of what seems like an abnormal result: Sample sites are indicated with the red circles with their value in bold italic face. The IDW cell values are indicated in the cell center. Could anyone explain why is there a cell with a value of 353 in that cell by the center of the figure, when there are no high values in the vicinity. What is the source of this artifact? Thanks for your help.