Vary transparency by attribute

Transparency is a blend mode that reduces the visibility of the symbology to allow content lower in the drawing order to show through. In most cases, transparency is needed to show the geographic data underneath. You can achieve this goal by setting transparency universally on a layer.

You can also vary transparency by an attribute or an expression. Varying the transparency of symbols is a way to indicate variations in magnitude of an attribute. For example, polygon symbols representing election results can have transparency set relative to the percentage of the total population that cast a ballot.

This map uses transparency as a visual variable against graduated colors symbology to emphasize more heavily populated districts.

You can vary the transparency of any primary symbology that supports varying symbology by attribute. You can also adjust the transparency of any color in any symbol. Alternatively, you can apply a layer or feature blend mode visual effect to your symbology, which mixes the color values of your symbology with the background.

Caution:

While you can combine these approaches in a map, the result may be difficult to understand visually. For example, because transparency is a blend mode, two features with the same transparency value may draw differently because of the color of the contents underneath.

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Learn more about working with color and transparency

Learn more about blend modes and layer blending

Set the transparency of a layer universally

To set the transparency of a layer universally, complete the following steps:

1. Select a feature layer in the Contents pane.
2. On the Feature Layer tab, in the Effects group, adjust the Layer Transparency slider or type a transparency percentage.

Set the transparency variable to a field or an expression

You can refine layer symbology by setting the transparency variable to a field or an expression.

Note:

When working with graduated symbols or proportional symbols symbology, the transparency variable applies to the template (point) symbol, not to the background (polygon) symbol.

1. Select the feature layer in the Contents pane.
2. On the Feature Layer tab, in the Drawing group, click Symbology .
3. In the Symbology pane, on the Vary symbology by attribute tab , expand the Transparency heading and do one of the following:
   • Choose a numeric field from the Field menu to vary the transparency.
   • Write an expression to determine transparency. Choose Custom from the Field menu, or click the Set an expression button to open the Expression Builder dialog box. Write an expression and click Verify to validate it. Note that although an expression is valid, it may not return a valid numeric value for the transparency variable. You can filter the Expression Builder dialog box to show only numeric fields to help prevent this.

     Learn more about writing expressions in the Arcade language.

4. Optionally, choose a Normalization field. Normalization is only available when the transparency variable is set to a field. It is not available when the transparency variable is set to an expression.
5. Specify the high and low values and optionally adjust the histogram. See Histograms for more information.
6. Check the Show legend check box to add a representation of the transparency variation to the layer's legend in both the Contents pane and any legends placed on layouts.
7. To remove the transparency variable or the normalization field, choose <none> from the Field or Normalization menus, respectively.

Caution:

Expressions are not saved by the layer if you change the transparency variable to read from a field instead of an expression. You can save the expression from the Expression Builder dialog box by clicking Export before making changes.