Unclassified Quantitative Symbology for Vector Features
Included in this tutorial
Accessing the Categorical Symbology options, with point features
Employing categorical symbols based on one or more fields
Formatting categorical symbols, in the Symbol Format Gallery
Additional examples with polylines and polygons
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 quantitative values without classification, using the standard data package in Tutorial Data. For this demonstration, we will use both point features and polygon features.
Related tutorials
The equivalent tutorial for classified values is Classified Quantitative Symbology for Vector Features.
The equivalent tutorial to unclassified colors for raster datasets is Unclassified Quantitative Symbology for Rasters (”Stretched” Colors).
Accessing unclassified 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 an unclassified option from the Primary Symbology drop-down menu.
accessing the Symbology panel by right-clicking on a layer’s name in the Contents panel
Unclassed Colors
Unclassified colors use a “stretched” color ramp, assigning colors from the minimum to the maximum value along the ramp. This means that features will have slightly different colors depending on their attribute value, with as many different colors on the map as there are unique values within the field in the attribute table.
The following demonstrations walk through accessing the options for unclassed colors, first for points and then for polygons. The options are similar for polyline layers, with the exception that they lack a fill color.
(In these demonstrations, right-clicks are shown in yellow and left-clicks are shown in magenta.)
Unclassed Colors for Point Layers
After accessing the symbology options for unclassed colors,
Choose the field with the values you want to symbolize. Notice that the Field drop-down menu only lists numeric attribute fields for quantitative symbologies.
If you would like to normalize your values based on another attribute field, you can choose that field in the Normalization drop-down.
The Color Scheme, Upper and Lower Labels, and Template options allow you to control the display of the symbol. The symbol template swatch can be changed through similar options and properties as the single-symbol options. (You can find more here: Single Symbols for Vector Features.)
The “More” dropdown includes other options, including inspecting the basic descriptive statistics for the values in the chosen field.
As with other symbology approaches, the panel includes several options at the top. We encourage you to inspect these further. A few are highlighted in the demonstration, including additionally varying the size of each symbol based on a field in the attribute table.
applying unclassified color symbols to point features
Unclassed Colors for Polygon Layers
The steps for applying unclassified colors for polygon or polyline layers are very similar (practically identical) to those for working with a point layer. These are reviewed again in the demonstration below.
Notice that this demonstration picks up where the last one leaves off. As a result, we do not need to right-click on the layer’s name to access the Symbology panel. Instead, we simply have to highlight the appropriate layer in the Contents panel, and the Symbology options update to reflect those for the currently highlighted layer.
One additional option available with polygons: Notice that the Color Scheme options include a settings “gear” button to specify whether to apply the scheme to the features’ fill, outline, or both.
applying unclassified color symbols to polygon features
Proportional Symbols
Proportional symbols are similar to unclassified colors in that they represent each feature with unique symbol properties based on the values in an attribute field. Whereas “unclassed colors” uses a color ramp, proportional symbols are sized in proportion to the attribute values.
For this demonstration, we will use the same Points1_Table1_join layer to show different options based on the Int_sm field (normalized by the Int_lrg field).
In order, the demonstration walks through:
Choosing Proportional Symbols as the Primary Symbology in the Symbology pane.
Specifying the “Int_sm” field in the Field drop-down: the values in this field will be used to size each symbol.
Quickly changing the symbol template to a lighter color (so we can see the symbols on our map because the default color was quite dark).
Normalizing the values in the Int_sm field by the “Int_lrg” field by choosing the latter in the Normalization drop-down. Now our map uses the quotient “Int_sm / Int_lrg” as the value that determines the size of each symbol. This change is also reflected in the working legend on the Contents panel.
By default, these symbols are sized based on “Unknown Units.” In other words, the size of each symbol is scaled between a minimum size and a maximum size which you can specify within the Primary Symbology panel.
Alternatively, you can assign the values a linear unit of measure (e.g., feet or meters), and map the symbols to scale.
Change the Unit to kilometers, which will map the symbol based on the attribute value in scaled units.
Assign the features’ value to the radius of the symbol rather than its area.
Toggle between circular symbols and square symbols with the Symbol Form option.
Change the symbols’ outline color and thickness. Then change the symbols’ fill color transparency.
Lastly, the demonstration quickly indicates where additional options can be found within the interface (most are applicable to other symbology types as well), including excluding some values from the map based on an expression using attribute values.
applying proportional symbols to point features
Proportional Symbols with other vector types
You can apply proportional symbols to other vector types (for example, polygon options at right).
In the cases of polygon features, the symbol will be mapped at the centroid of each feature. Polyline features will be symbolized with varying thicknesses.
Dot Density symbology
Dot density maps fill polygon features with dots representing a quantity from the layer’s attribute table.
Usually, this is done through assigning each dot an incremental value. For example, 1 dot = 10 people within the area enclosed by a polygon. The dots do not directly correspond to location (they are generally randomly placed within the polygon), and thus care should be taken to avoid graphically suggesting that the location of a dot represents the precise location of the value it represents.
The demonstration below shows:
Choosing Dot Density as a polygon layer’s primary symbology.
Specifying a field as the values to represent with dots per polygon. (In this example, we choose the “Int_sm” field again.)
Changing the Dot Value option. The “Dot Value” is the x in “1 Dot = X.” Notice that this will also update in the working legend within the Contents panel.
Changing the symbol applied to each polygon as the background behind the dots. (You can think of this as a single symbol in combination with the dot density.)
Specifying the unit label per dot. In this example, we choose “People.” Notice this too will update within the Contents panel.
Dot densities are particularly useful when visualizing quantities in different categories. If, for example, the values in the “Int_sm” field represent the number of people belonging to Group A and the values in the “Int_lrg” field represent the number of people belonging to Group B, then we can represent both quantities as dots of different colors.
Changing the Symbol Label. Here, we specify that the “Int_sm” field represents the number of people within “Group A.”
Adding the “Int_lrg” field to the list of fields included in the map, and changing its symbol label as well.
Other adjustments: Notice that the dot value changes automatically to accommodate the much larger values in this field. Thus, the demonstration includes changing the dot value manually once again. In addition, we change the color scheme, the dot size for both dots, and the symbol color for just one field.
applying a dot density symbology to polygon features with two attribute fields