kriging spatial analyst
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PERFORMINGSPATIALANALYSIS 147
Creating a surface usingkriging interpolation witha variable radius
1. Click the Spatial Analystdropdown arrow, point toInterpolate to Raster, andclick Kriging.
2. Click the Input pointsdropdown arrow and clickthe point dataset you wish touse.
3. Click the Z value fielddropdown arrow and clickthe field you wish to use.
4. Click the Kriging method youwish to use.
5. Click the Semivariogrammodel dropdown arrow andclick the model you wish to
use.6. Click the Search radius type
dropdown arrow and clickVariable.
7. Optionally, change thedefault number of points.
8. Optionally, specify a maxi-mum distance.
9. Optionally, change thedefault Output cell size.
10. Optionally, check CreatePrediction of standard error.
11. Specify a name for theOutput raster or leave thedefault to create a temporarydataset in your working
directory.
12. Click OK.
Kriginginterpolation
There are two kriging methods:Ordinary and Universal.
Ordinary kriging is the mostgeneral and widely used of thekriging methods and is thedefault. It assumes the constantmean is unknown. Universalkriging should only be used
when you know there is a trendin your data and you can give ascientific justification todescribe it.
By using a variable searchradius, you can specify thenumber of points to use incalculating the value of theinterpolated cell. This makes thesearch radius variable for eachinterpolated cell, depending onhow far it has to stretch toreach the specified number ofinput points.
Specifying a maximum distancelimits the potential size of theradius of the circle. If the
number of points is not reachedbefore the maximum distance ofthe radius is reached, fewerpoints will be used in thecalculation of the interpolatedcell. u
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148 USING ARCGIS SPATIAL ANALYST
Creating a surface usingkriging interpolation witha fixed radius
1. Click the Spatial Analystdropdown arrow, point toInterpolate to Raster, andclick Kriging.
2. Click the Input pointsdropdown arrow and click thepoint dataset you wish to use.
3. Click the Z value field
dropdown arrow and click thefield you wish to use.
4. Click the Kriging method youwish to use.
5. Click the Semivariogrammodel dropdown arrow andclick the model you wish touse.
6. Click the Search radius typedropdown arrow and clickFixed.
7. Optionally, change thedefault distance for thesearch radius setting.
8. Optionally, change theminimum number of points.
9. Optionally, change thedefault Output cell size.
10. Optionally, check CreatePrediction of standard error.
11. Specify a name for theOutput raster or leave thedefault to create a temporarydataset in your working
directory.
12. Click OK.
With a Fixed radius, the radiusof the circle used to find inputpoints is the same for eachinterpolated cell. The default
radius is five times the cell sizeof the output raster. By specify-ing a minimum number ofpoints, you can ensure thatwithin the Fixed radius, at leasta minimum number of inputpoints will be used in thecalculation of each interpolatedcell.
Tip
Deciding on the radius or
the number of points
Use the Measure tool on the Tools
toolbar to measure distance
between points to get an idea of theradius and number of points to use.
Tip
Changing the lag size,
major range, partial sill,
and nugget
Click Advanced Parameters on the
Kriging dialog box to specify these
parameters if they are known;otherwise, Spatial Analyst will
estimate them for you.
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