Pitney Bowes MapInfo Vertical Mapper - Manual (Page 48)

Kriging Interpolation
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Vertical Mapper 3.7
Decay Curves used by IDW interpolation.
The disadvantage of IDW interpolation is that it treats all points that fall within the search radius the
same way.
For example, if an exponent of 1 is specified, a linear distance decay function is used to determine
the weights for all points that lie within the search radius. This same function is used for all points
regardless of their geographic orientation to the node (north, south, etc.) unless a sectored search is
implemented.
Kriging, on the other hand, uses different weighting functions depending on the distance and
orientation of sample points with respect to the node and the manner in which sample points are
clustered.
This figure illustrates the influence points have, using IDW interpolation, on the
calculated value based on the same distance decay function when one of the points is
northeast of the grid node (point A) and the other point is southeast (point B). With
kriging, the grid node may be calculated using a different weighting function for every
point in the search radius.
Before interpolation begins, every possible distance weighting function is calculated by generating
an experimental semivariogram and choosing a mathematical model to approximate its shape. The
mathematical model provides a smooth, continuous function for determining appropriate weights for
increasingly distant data points.