ArcGIS Pro: The number of classes must be an integer between 2 and 32

Error Message

In ArcGIS Pro, symbolizing a geostatistical layer with more than 32 classes fails and the following error message is returned in the Symbology pane:

Error: 
The number of classes must be an integer between 2 and 32.

Cause

Geostatistical layers are dynamically rendered from interpolation models and do not store values as static data. Their symbology is generated on the fly as vector contours, and increasing the number of classes raises the computational load required to render and update the layer. To maintain performance and responsiveness, ArcGIS Pro set the maximum number of classes to 32.

Solution or Workaround

To resolve this issue, export the geostatistical layer to a raster or contour layer, which allows symbolization with more than 32 classes.

Export geostatistical layer to raster layer

1. Open the project in ArcGIS Pro.
2. Right-click the geostatistical layer in the Contents pane and select Export Layer > To Rasters.
3. In the GA Layer To Rasters pane, configure the following parameters:
   1. For Input geostatistical layer, select the input geostatistical layer. In this example, Kriging is selected.
   2. For Output Surface Type, select the preferred surface type. In this example, Prediction is selected.
   3. For Output raster, specify the preferred output raster name and location to export. In this example, the name is GA_to_Raster.
   4. Click Run.

4. In the Contents pane, right-click the output raster and select Symbology.
5. In the Symbology pane, for the Classes field, specify the preferred number of classes. In this example, it is specified as 34.
6. Close the Symbology pane.

The map below shows the raster layer exported from a geostatistical layer and symbolized using 34 classes.

Export geostatistical layer to contour layer

1. Open the project in ArcGIS Pro.
2. Right-click the geostatistical layer in the Contents pane and select Export Layer > To Contours.
3. In the GA Layer To Contour pane, configure the following parameters:
   1. For Input geostatistical layer, select the input geostatistical layer. In this example, Kriging is selected.
   2. For Contour Type, select a contour type. In this example, Same as layer is selected.
   3. For Output feature class, specify the preferred output name and location to export. In this example, the name is GA_to_Contour.
   4. For Contour quality, select a contour quality. In this example, Draft is selected.
   5. Expand Classification and specify the Classification type; in this example, Geometric Interval is selected. For Number of classes, specify the preferred number of classes; in this example, it is specified as 34.
   6. Click Run.

4. Right-click the output contour layer in the Contents pane and select Symbology. The number of symbol classes is shown at the bottom of the Symbology pane.
5. Close the Symbology pane.

The map below shows the contour layer exported from a geostatistical layer and symbolized using 34 classes.