This sample demonstrates how to use opacity to visualize an attribute value, in this case median household income.

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          // use opacity to visualize median household income
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          visualVariables: [
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            {
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              type: "opacity",
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              field: "MEDHINC_CY",
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              stops: [
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                { value: 10000, opacity: 0.2, label: "$10,000" },
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                { value: 100000, opacity: 0.85, label: "$100,000" },
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              ],
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            },
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          ],

Any combination of visual variables may be used to add context or draw more attention to spatial patterns in a dataset. In this case, opacity is the only visual variable used in the renderer. However, opacity, size, and color visual variables may all be applied to a renderer to create multivariate visualizations.

Additional visualization samples and resources