Creating maps using kernel interpolation with barriers

Available with Geostatistical Analyst license.

Kernel interpolation with barriers is a method that is similar to local polynomial interpolation, but it can account for barriers within the study area. This allows you to, for example, interpolate water contaminant levels within a lake and obtain more accurate estimates close to an irregularly shaped shore than you would by using methods that do not adjust for barriers.

1. Click the point layer in the ArcMap table of contents that contains the attributes you are interested in.

   Alternatively, go directly to step 2 and browse to the dataset you are interested in on the first page of Geostatistical Wizard.

2. Start Geostatistical Wizard.
3. Under the Methods section, choose Kernel Smoothing, which is located under Interpolation with barriers.

   The lower portion of Geostatistical Wizard shows information about Kernel Interpolation with Barriers. There is also a link that will take you directly to more detailed information on this method in the main help system.

4. Under the Input Data section, you should see that Source Dataset has been set to the layer you clicked in the ArcMap table of contents. Under Data Field, choose the attribute that you want to interpolate.

   In addition, you can specify a Weight field. This will weigh the data values and alter the interpolated surface. Including a weight can be a useful option when you want to include a measure of confidence in the data (for example, GPS locations taken inside a forest may be less reliable than those taken in clear areas, so you might choose to assign them less weight in the interpolation).

5. Under the Barrier features section, choose the polygon or polyline feature layer that you want to use as a barrier.

   This method can also be used without specifying a barrier dataset.

6. Click Next.
7. Choose a value for Kernel Function: Exponential, Gaussian, Quartic, Epanechnikov, Polynomial Order 5, and Constant.
8. Modify Order of Polynomial, which can be either 0 or 1.

   Step 2 of Geostatistical Wizard is where the parameter values for this method must be defined. For kernel interpolation with barriers, the parameters that you can change are Kernel Function, Order of Polynomial, Ridge, and Bandwidth. You can investigate the effects of changing the values for these parameters by examining the preview surface and evaluating the quality of fit of the model on the next page of Geostatistical Wizard.

9. If Order of Polynomial is set to 1, Output Surface Type can be set to Prediction (to preview and generate a map of predicted values) or to Prediction Standard Error (to assess the uncertainty associated with the predicted values).
10. Click Next.
11. Assess the quality of fit of the model using the Predicted and Error graphs and the summary information on Prediction Errors and by examining particular pairs of measured and predicted values in the table on the left-hand side.
12. Once you are satisfied with the model, click Finish. A Method Report window appears.
13. Click OK to produce the surface.

    The Method Report window contains a summary showing the dataset, attribute, interpolation method, and parameter values used to create the surface. This information can be retrieved for any geostatistical layer by right-clicking it in the ArcMap table of contents, choosing Properties from the menu, then clicking the Method Summary tab.

The result is a surface generated by interpolating attribute values using kernel interpolation with barriers. The surface is added directly to the ArcMap table of contents and displayed using a default color scheme and class breaks, which can be changed by accessing the layer's properties.