Classified Quantitative Symbology for Vector Features
Included in this tutorial
Accessing vector symbology options from the Contents pane.
Graduated colors symbology, with a polygon layer example
Graduated symbols symbology, with a point layer example
Software version in examples: ArcGIS Pro 2.9.1
Tutorial Data: The tutorial includes demonstration with sample data available here.
Credits: L. Meisterlin (2022)
This tutorial demonstrates different symbology approaches for visualizing classified quantities, using the standard data package in Tutorial Data. For this, we use polygon features to create a choropleth map with graduated colors and point features to apply graduated symbols to features.
Related Tutorials:
The equivalent tutorial for unclassified values is Unclassified Quantitative Symbology for Vector Features.
The tutorial that demonstrates different classification methods in ArcGIS Pro is Classifying Features by Quantitative Attribute Values.
For large datasets, you may need to change the maximum sample size that your software uses to generate histograms and calculate break values. See Changing the Maximum Sample Size (Quantitative Symbology Options).
Accessing classified quantitative symbology options
To access the symbology options, open the Symbology panel by right-clicking on the layer’s name in the Contents panel and choosing Symbology.
This will summon the Symbology panel, where you can choose a classified option from the Primary Symbology drop-down menu.
accessing the Symbology panel by right-clicking on the layer’s name in the Contents panel
Graduated Colors
We can apply graduated colors to classified quantities based on values in a layer’s attribute table. This means that values are grouped into classes and each class is assigned a color, generally along a color ramp that corresponds to the ascending or descending values per class. Features with values within the same class will be symbolized with the same color.
The software interactions demonstrated here are the same for applying graduated colors to polyline or point feature classes, as well.
After accessing the symbology options for graduated colors, the demonstration (below) shows the following:
Choosing the numeric field from the layer’s attribute table containing the values we want to classify and symbolize. In this example, we choose the “Int_lrg” field. Notice that only numeric fields are listed for quantitative symbology approaches.
We will not normalize these values by another field in the layer’s attribute table, but the drop-down options to do so are located beneath the Field drop-down. Again, only numeric fields are listed.
Choose the Classification Method and number of classes. In this example we will map these polygons’ attribute values in quartiles: four classes each containing the same number of features. Thus the lowest class contains the polygons in the “bottom 25%” and the highest class contains those in the “top 25%.” For more on classification methods, see Classifying Features by Quantitative Attribute Values.
Choosing a Color Scheme from the pre-set drop down menu of choices, then inspecting the results.
Each class is listed with its Symbol swatch, the upper value of the class range, and the label used within the legend. The Label is editable, and we demonstrate changing the first label to say “Bottom 25%.” Notice that this is updated in the working legend in the Contents panel.
Accessing the histogram and displaying the descriptive statistics that summarize the values in the chosen field.
Additional options for customizing colors: accessing the Color Scheme Editor; applying colors to the polygons’ fill, outline, or both; changing the formatting for all symbols; and changing the formatting for only one symbol.
Lastly, we walk through the various other options at the top of the Symbology panel, including changing the order in which features are rendered based on their symbol/class.
NOTE: In these demonstrations, left-clicks are shown in magenta and right-clicks are shown in yellow.
applying graduated colors to symbolize polygon features
Graduated Symbols
Like graduated colors, we can also apply graduated symbols to classified quantities based on values in a layer’s attribute table. Rather than assigning a color (although you certainly could), the features grouped into each class is assigned a size. Usually, these sizes increase or decrease with the range represented per class.
In the demonstration below, we will apply graduated symbols to point features. The software interactions are similar for other geometry types, for which the symbol would be located at each feature’s centroid.
After accessing the symbology options for graduated symbols, the demonstration (below) shows the following:
Choosing the attribute field(s) with values to symbolize. Here we use the values in the “Int_sm” field, normalized by the values in the “Int_lrg” field. (Thus, the values represented on the map will be the quotient “Int_sum / Int_lrg.”)
Choose the Classification Method. Above we demonstrated a method that requires specifying the number of classes. Here, we choose the Defined Interval method which requires specifying the range (size of the interval) per class. For more on classification methods, see Classifying Features by Quantitative Attribute Values.
Then, we walk through several of the options to customize the symbols: changing the minimum and maximum size of the symbol (the symbols applied per class are proportionately rendered between these sizes by default, but can also be individually adjusted); adjusting the template swatch applied to all symbols; adjusting the appearance of only one symbol.
Lastly, the demonstration clicks through the other options listed within the pages of the Symbology panel.
applying graduated symbols to point features