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View Opacity based unique value renderer sample in sandbox
Opacity based unique value renderer

Description

Renderer.setOpacityInfo() allows you to render quantitative data with a color ramp (continuous color) using varying opacity. (Added at version 3.11 of the JS API)

Code

<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no" />
    <title>Predominant Crop Opacity</title>
    <link rel="stylesheet" href="https://js.arcgis.com/3.20/dijit/themes/claro/claro.css">
    <link rel="stylesheet" href="https://js.arcgis.com/3.20/esri/css/esri.css" />
    <style>
      html, body, #map {
        height: 100%;
        margin: 0;
        background-color: #000000;
      }

      .esriAttribution {
        background: none;
        color: #ffffff;
      }

      #info {
        width: 14.0625em;
        background-color: #000;
        color: #fff;
        position: absolute;
        left: 0;
        bottom: 0;
        padding-left: 10px;
        padding-top: 10px;
        font-family: Arial, "Helvetica Neue", Helvetica, sans-serif;
        border-top: 2px solid #ffffff;
        border-right: 2px solid #ffffff;
        border-top-right-radius: 20px;
      }
    </style>

    <script src="https://js.arcgis.com/3.20/"></script>

    <script>
      var map;
      require([
        "dojo/_base/array",
        "dojo/number",
        "esri/Color", "esri/dijit/Legend",
        "esri/geometry/Extent", "esri/InfoTemplate", "esri/layers/FeatureLayer",
        "esri/map", "esri/renderers/UniqueValueRenderer",
        "esri/symbols/SimpleFillSymbol", "esri/symbols/SimpleLineSymbol", "dojo/domReady!"
      ], function (array, number, Color, Legend, Extent, InfoTemplate, FeatureLayer, Map, UniqueValueRenderer,
        SimpleFillSymbol, SimpleLineSymbol){

        map = new Map("map", {
          minScale: 18489297,
          maxScale: 1245436,
          extent: new Extent({
            "xmax": -7218373,
            "xmin": -15045524,
            "ymax": 7571201,
            "ymin": 2160682,
            "spatialReference": { "wkid": 102100}
          })
        });

        // --------------------------------------------------------------------
        // Custom function to format the numbers for crop values
        // e.g., 126744 becomes 126,744
        // --------------------------------------------------------------------
        formatNumber = function (value, key, data){
          return number.format(value, {places: 0, locale: "en-us"});
        };

        var featureLayerOptions = {
          mode: FeatureLayer.MODE_AUTO,
          outFields: ["M163_07", "M172_07", "M188_07", "M193_07", "M217_07", "COUNTY", "STATE", "AREA", "M086_07"],
          infoTemplate: new InfoTemplate("${COUNTY}, ${STATE}",
            "<b>Corn for grain:</b> ${M163_07:formatNumber}<br><b>All wheat for grain:</b> ${M172_07:formatNumber}<br><b>Upland cotton:</b> ${M188_07:formatNumber}<br><b>Soybeans for beans:</b> ${M193_07:formatNumber}<br><b>Vegetables:</b> ${M217_07:formatNumber}")
        };
        var featureLayer = new FeatureLayer("//services.arcgis.com/V6ZHFr6zdgNZuVG0/ArcGIS/rest/services/USA_County_Crops_2007/FeatureServer/0",
          featureLayerOptions);

        // --------------------------------------------------------------------
        // Custom function to compute the crop that has the largest value
        // in a particular count. Using a custom function with a renderer
        // is a really powerful method of having control over symbology
        // client-side, especially if you don't have control over the service.
        // --------------------------------------------------------------------
        var uniqueValueRenderer = new UniqueValueRenderer(createSymbol("#d9d9d9"), function (graphic){
          var maxField = "Other";
          var max = 0;

          array.forEach(featureLayerOptions.outFields, function (field){
            if (graphic.attributes[field] > max) {
              maxField = field;
              max = graphic.attributes[field];
            }
          });

          return maxField;
        });

        // --------------------------------------------------------------------
        // Helper function for creating symbols for the UniqueValueRenderer
        // --------------------------------------------------------------------
        function createSymbol(color){
          return new SimpleFillSymbol()
            .setColor(new Color(color))
            .setOutline(
            new SimpleLineSymbol().setColor(new Color("#999999")).setWidth(1)
          );
        }

        uniqueValueRenderer.addValue({ value: "M217_07", symbol: createSymbol("#fd7f6f"), label: "Vegetables" });
        uniqueValueRenderer.addValue({ value: "M188_07", symbol: createSymbol("#b2e061"), label: "Cotton" });
        uniqueValueRenderer.addValue({ value: "M172_07", symbol: createSymbol("#bd7ebe"), label: "Wheat" });
        uniqueValueRenderer.addValue({ value: "M193_07", symbol: createSymbol("#7eb0d5"), label: "Soybeans" });
        uniqueValueRenderer.addValue({ value: "M163_07", symbol: createSymbol("#ffb55a"), label: "Corn" });

        // --------------------------------------------------------------------
        // Use the average data values to control opacity
        // Field:       M086_07
        // Description: The acres of total cropland as a percentage of land area in acres.
        //
        // Standard Deviation:    28.9616022263796
        // Average:               39.457298802092
        // Standard Deviation -1: 10.495696576
        // Standard Deviation +1: 68.418901028
        //
        // For more information about statistics: see the outStatistics
        // parameter in the ArcGIS REST API Help.
        // --------------------------------------------------------------------
        uniqueValueRenderer.setOpacityInfo({
          field: "M086_07",
          stops: [
            { value: 10, opacity: 0   }, // -1 stddev,     transparent
            { value: 39, opacity: 0.5 }, // average value, 50% transparent
            { value: 68, opacity: 1   }  // +1 stddev,     completely opaque
          ]
        });

        featureLayer.setRenderer(uniqueValueRenderer);
        map.addLayer(featureLayer);

        var legend = new Legend({
          map: map,
          layerInfos: [
            {
              layer: featureLayer,
              title: "Acres harvested by type"
            }
          ]
        }, "legend");

        legend.startup();
      });
    </script>
  </head>

  <body>
    <div id="map"></div>
    <div id="info">
      <div id="legend"></div>
    </div>
  </body>
</html>