Categorical (Unique Values) Symbology for Raster Datasets
Included in this tutorial
Accessing symbology options
Applying unique values symbology
Bonus: Don’t do this with categorical or qualitative attribute values!
Software version in examples: ArcGIS Pro 3.0.0
Tutorial Data: The tutorial includes demonstration with sample data available here.
Credits: L. Meisterlin with Varisa Tanti (2022)
Categorical symbology approaches visualize data based on individual, unique values or by categorized types.
This tutorial walks through applying a “unique values” symbology to the values in a raster dataset in ArcGIS Pro, using a raster dataset produced with the tract layers in the Tutorial Data Standard Data Package.
Accessing Symbology options
access the Symbology panel by right-clicking on a layer’s name in the Contents panel
Access the symbology panel by right-clicking the relevant layer’s name in the Contents panel and choosing Symbology.
If the Symbology panel is already open, you can access the symbology options of a particular layer by selecting it in the Contents panel.
Applying Unique Values Symbology
To change the symbology approach to categorical symbology, click the Primary Symbology drop-down menu within the Symbology panel and select “Unique Values.”
in the Primary Symbology drop-down menu, select “Unique Values”
Once Unique Values is selected, the options of the Symbology panel should be fairly familiar to you. For more, see the tutorial on Categorical Symbols for Vector Features.
You can access the color options by double-clicking on individual swatches.
You can assign text labels to represent or decode the numeric values in your legend.
As a reminder, categorical symbology assigns a color for each unique type (value) in the chosen field. It is best to use different colors (different hues, not different intensities of the same hue—see below) because the cell values represent different “types” rather than different “amounts.”
Bonus: Don’t do this with categorical or qualitative attribute values…
Here’s an example of what not to do. The field being symbolized has qualitative attributes (i.e., “types of stuff” rather than “amounts of stuff”), although they are coded with numeric values within our raster dataset. Using a graduated ramp symbology can be misleading, implying that the cell’s values were measurable or quantitatively comparable (or, even, arranged in a hierarchy ranging from “more” to “less”).
Using a graduated color ramp symbology can be misleading for categorical data—implying there were some kind of hierarchy of measurable values