opacity | API Reference | ArcGIS Maps SDK for JavaScript 4.31

See also

Styles and data visualization

Method Overview

Name	Return Type	Summary	Object
	Promise<VisualVariableResult>	This method generates an opacity visual variable with default alpha values optimally mapped to data values based on the statistics queried for the indicated field or expression.	opacity

Method Details

createVisualVariable Method createVisualVariable(params){Promise<VisualVariableResult>}

This method generates an opacity visual variable with default alpha values optimally mapped to data values based on the statistics queried for the indicated field or expression.

There are several ways this method may be called. The most common case is by providing a layer and a field. This is the scenario where the statistics of the data aren't well known and the user doesn't know the which alpha values to map to data values. You can optionally use a valueExpression instead of a field to visualize features based on a numeric value returned from a script executed at runtime.

The other options are provided for convenience for more involved custom visualization authoring applications. For example, if you already generated statistics in another operation, you can pass the stats in the statistics parameter to avoid making an extra call to the server.

Parameters

Specification

params Object

Input parameters for generating an opacity visual variable based on data returned from a given field or expression. See the table below for details of each parameter.

Specification

The layer for which the visual variable is generated.

field String

optional

The name of the field whose data will be queried for statistics and used for the basis of the data-driven visualization. This property is ignored if a valueExpression is used.

normalizationField String

optional

The name of the field to normalize the values of the given field. Providing a normalization field helps minimize some visualization errors and standardizes the data so all features are visualized with minimal bias due to area differences or count variation. This option is commonly used when visualizing densities.

valueExpression String

optional

An Arcade expression following the specification defined by the Arcade Visualization Profile. Expressions may reference field values using the $feature profile variable and must return a number. This property overrides the field property and therefore is used instead of an input field value.

valueExpressionTitle String

optional

Text describing the value returned from the valueExpression. This is used by the Legend widget.

sqlExpression String

optional

A SQL expression evaluating to a number.

sqlWhere String

optional

A SQL where clause used to filter features for the statistics query. For example, this is useful in situations where you want to avoid dividing by zero as is the case with creating a predominance visualization.

filter FeatureFilter

optional

Since 4.31 When defined, only features included in the filter are considered in the attribute and spatial statistics calculations when determining the final renderer. This is useful when a lot of variation exists in the data that could result in undesired data ranges. A common use case would be to set a filter that only includes features in the current extent of the view where the data is most likely to be viewed. Currently, only geometry filters with an intersects spatial relationship are supported. All other filter types (including where) are ignored.

legendOptions Object

optional

Provides options for setting a title to a field when an expression is provided instead of a field name. This title will represent the field in the Legend.

Specification

title String

optional

The title used to represent the given field or expression in the Legend.

statistics SummaryStatisticsResult

optional

A statistics object generated from the summaryStatistics function. If statistics for the field have already been generated, then pass the object here to avoid making a second statistics query to the server.

minValue Number

optional

A custom minimum value set by the user. Use this in conjunction with maxValue to generate statistics between lower and upper bounds. This will be the lowest stop in the returned visual variable.

maxValue Number

optional

A custom maximum value set by the user. Use this in conjunction with minValue to generate statistics between lower and upper bounds. This will be the uppermost stop in the returned visual variable.

view View

optional

A SceneView or MapView instance is required when a valueExpression is specified.

forBinning Boolean

optional

Indicates whether the generated renderer is for a binning visualization. If true, then the input field(s) in this method should refer to aggregate fields defined in the featureReduction property of the layer.

signal AbortSignal

optional

Allows for cancelable requests. If canceled, the promise will be rejected with an error named AbortError. See also AbortController.

Returns

Type	Description
Promise<VisualVariableResult>	Resolves to an instance of VisualVariableResult.

Examples

let layer = new FeatureLayer({
  url: "https://services.arcgis.com/V6ZHFr6zdgNZuVG0/arcgis/rest/services/counties_politics_poverty/FeatureServer/0"
});

// visualization based on field and normalization field
let params = {
  layer: layer,
  field: "POP_POVERTY",
  normalizationField: "TOTPOP_CY"
};

// when the promise resolves, apply the visual variable to the renderer
opacityVariableCreator.createVisualVariable(params)
  .then(function(response){
    let renderer = layer.renderer.clone();
    renderer.visualVariables = [ response.visualVariable ];
    layer.renderer = renderer;
  });

let layer = new FeatureLayer({
  url: "https://services.arcgis.com/V6ZHFr6zdgNZuVG0/arcgis/rest/services/counties_politics_poverty/FeatureServer/0"
});

// visualization based off Arcade expression
let params = {
  layer: layer,
  valueExpression: "($feature.POP_POVERTY / $feature.TOTPOP_CY) * 100",
  view: view,
  valueExpressionTitle: "% of people living in poverty"
};

// when the promise resolves, apply the visual variable to the renderer
opacityVariableCreator.createVisualVariable(params)
  .then(function(response){
    let renderer = layer.renderer.clone();
    renderer.visualVariables = [ response.visualVariable ];
    layer.renderer = renderer;
  });

Type Definitions

VisualVariableResult Type Definition VisualVariableResult

The result object of the createVisualVariable() method. See the table below for details of each property.

Properties: visualVariable OpacityVariable

An opacity visual variable configured based on the statistics of the data.

statistics SummaryStatisticsResult

Basic statistics returned from a query to the service for the given field or expression.

defaultValuesUsed Boolean

Indicates whether default values are used in the absence of sufficient data and/or statistics from the layer. Default values are typically used when all features have the same field value or no value at all.

authoringInfo AuthoringInfo

Authoring information related to the creation of the visual variable. This includes information related to UI inputs from sliders and selected themes.