I'm trying to find the best interpolation method for a project I'm working on. I've tried the basic settings with spline, IDW & kriging and they all appear ok at first glance, but when I look more closely they don't follow the points exactly like they should. For example, I will have a point or cluster of points with a value of 59, and a neighboring point or cluster of points with a value of 60. When I adjust the symbology to 59.5 I would think the line would be drawn evenly between the two points or clusters of points every time. In some cases the line is drawn between the two, but in other cases it is not. The resulting map is "generally" correct, but with a lot of little errors here and there. I'm not real familiar with how interpolation works exactly, and I want to know if one of the methods would be more accurate or have less errors for the particular project I'm working on. I will have 20,000+ points over an area the size of Florida (if that even matters).

Mike

As far as exact interpolation, please reference the following image. 2 cells of a raster, white equals the cell center and red is the sample location.

Predictions are made at the cell center and that value is assigned to the whole cell.

When predicting the value for the upper cell, 1395 will carry the most weight and therefore the cell's value will not be equal to 1395. However, 3199 falls exactly at the center of the cell and therefore that cell's predicted value will be equal to 3199.

The smaller the cell size the closer the predicted cell value will be to that of the sample point

Regards

-Steve