DotDensityRenderer

AMD: require(["esri/renderers/DotDensityRenderer"], (DotDensityRenderer) => { /* code goes here */ });
ESM: import DotDensityRenderer from "@arcgis/core/renderers/DotDensityRenderer";
Class: esri/renderers/DotDensityRenderer
Inheritance: DotDensityRenderer Renderer Accessor
Since: ArcGIS Maps SDK for JavaScript 4.11

DotDensityRenderer allows you to create dot density visualizations for polygon layers. Dot density visualizations randomly draw dots within each polygon to visualize the density of a population or some other variable. Each dot represents a fixed numeric value of an attribute or a subset of attributes. Unlike choropleth maps, field values used in dot density visualizations don't need to be normalized because the size of the polygon, together with the number of dots rendered within its boundaries, indicate the spatial density of that value.

For example, the image below visualizes population by Census tract using dot density. Notice that each dot represents about 100 people.

dot-density-one-attribute

You can specify multiple attributes to visualize subcategories of the data. For example, we can visualize the same layer above, but categorize each dot by race/ethnicity. So each dot of a different color represents 100 people of the respective category (e.g. 1 red dot represents 100 white non-Hispanic) people, each blue dot = 100 African American people, each yellow dot = 100 Hispanic people, etc).

dot-density

This implementation of dot density allows you to linearly scale the dot value based on the view scale. So as you zoom in and out of the initial view, the relative density of points remains the same across scales.

Keep in mind the following suggestions while creating dot density visualizations:

  • You should use Equal Area spatial references whenever possible, particularly when building dot density visualizations that span global extents. Using heavily distorted spatial references with a DotDensityRenderer is OK as long as you restrict the user from comparing the densities of features within the same view at large scales. We strongly discourage comparing features across multiple views when equal area projections cannot be used since significant differences in area distortion may cause the user to misinterpret feature density in heavily distorted areas.
  • You should typically set a minScale on the layer. Dot density visualizations are difficult to read when dots are no longer distinguishable either because they coalesce, or because they are too dispersed.
  • Setting a maxScale on the layer is also important because dot density maps tend to become unreadable at larger scales. Users may start seeing patterns in the random distribution of dots that do not exist in reality. They may also mistakenly interpret the location of each dot as an actual point feature. Users are particularly susceptible to this when the dotValue is set to 1. As an example, dot density visualizations on county datasets should only be viewed at the state or regional level.
  • Use the attributes property to specify one or more data values. When multiple attributes are specified, the group of attributes should make sense when visualized together, and generally should belong to a parent group. For example, you could map the density of pets, or the density of different kinds of pets such as dogs, cats, etc.
  • Use popups to clearly communicate the actual value of the feature, so the user can explore the map visually and interactively.

Known Limitations

See also
Example
layer.renderer = {
  type: "dot-density",  // autocasts as new DotDensityRenderer()
  dotValue: 1000,  // 1 dot = 1,000 people when the view.scale is 1:1,000,000
  referenceScale: 1000000,  // view.scale
  attributes: [{
    field: "ELEMENTARY_SCHOOL",
    label: "Elementary School",
    color: "red"
  }, {
    field: "MIDDLE_SCHOOL",
    label: "Middle School",
    color: "blue"
  }, {
    field: "HIGH_SCHOOL",
    label: "High School",
    color: "orange"
  }, {
    valueExpression: "$feature.ASSOCIATES_DEGREE + $feature.BACHELOR_DEGREE + $feature.MASTER_DEGREE + $feature.DOCTORATE_DEGREE",
    valueExpressionTitle: "People who completed university",
    label: "University"
    color: "green"
  }]
}

Constructors

new DotDensityRenderer(properties)
Parameter
properties Object
optional

See the properties for a list of all the properties that may be passed into the constructor.

Example
// Typical usage
let renderer = {
  type: "dot-density",  // autocasts as new DotDensityRenderer()
  dotValue: 1000,
  legendOptions: {
    unit: "people"
  },
  attributes: [{
    field: "Population",
    color: "yellow"
  }]
};

Property Overview

Any properties can be set, retrieved or listened to. See the Working with Properties topic.
Show inherited properties Hide inherited properties
Name Type Summary Class
AttributeColorInfo[]

Defines the variable(s) used to visualize density.

more details
DotDensityRenderer
AuthoringInfo

Authoring metadata only included in renderers generated from one of the Smart Mapping creator methods, such as sizeRendererCreator.createContinuousRenderer() or colorRendererCreator.createContinuousRenderer().

more details
Renderer
Color

The color used to shade the polygon fill behind the dots.

more details
DotDensityRenderer
String

The name of the class.

more details
Accessor
Boolean

Only applicable when two or more attributes are specified.

more details
DotDensityRenderer
Number

Defines the size of the dots in points.

more details
DotDensityRenderer
Number

Defines the initial dot value used for visualizing density.

more details
DotDensityRenderer
Object

An object providing options for configuring the renderer in the Legend.

more details
DotDensityRenderer
SimpleLineSymbol

The outline of the polygon.

more details
DotDensityRenderer
Number

When defined, the renderer will recalculate the dot value linearly based on the change in the view's scale using the calculateDotValue() method.

more details
DotDensityRenderer
Number

When set to a consistent value, dot placements will be preserved for the same scale given all parameters are the same in the renderer.

more details
DotDensityRenderer
String

The type of renderer.

more details
DotDensityRenderer
VisualVariable[]

An array of Size Visual Variable objects.

more details
DotDensityRenderer

Property Details

Defines the variable(s) used to visualize density. This is an array of objects, each of which references a numeric field value or Arcade expression used to drive the density. You must also set a color corresponding to each value.

If you set a single attribute, POPULATION and match it with a color black and the dotValue is 100, then number of black dots rendered for each feature will approximately equal the value of POPULATION divided by 100.

This property is limited to no more than 8 attributes.

See also
Example
renderer.attributes = [{
  field: "POPULATION",
  label: "Population (2019)",
  color: "gray"
}];

Authoring metadata only included in renderers generated from one of the Smart Mapping creator methods, such as sizeRendererCreator.createContinuousRenderer() or colorRendererCreator.createContinuousRenderer(). This includes information from UI elements such as sliders and selected classification methods and themes. This allows the authoring clients to save specific overridable settings so that next time it is accessed via the UI, their selections can be remembered.

backgroundColor Colorautocast
Autocasts from Object|Number[]|String

The color used to shade the polygon fill behind the dots. This can be autocast with a named string; hex string; array of rgb or rgba values; an object with r, g, b, and a properties; or a Color object.

Default Value:[0, 0, 0, 0.25] - black, semitransparent
Examples
// CSS color string
renderer.backgroundColor = "dodgerblue";
// HEX string
renderer.backgroundColor = "#33cc33";
// array of RGBA values
renderer.backgroundColor = [51, 204, 51, 0.3];
// object with rgba properties
renderer.backgroundColor = {
  r: 51,
  g: 51,
  b: 204,
  a: 0.7
};
declaredClass Stringreadonly inherited

The name of the class. The declared class name is formatted as esri.folder.className.

dotBlendingEnabled Boolean

Only applicable when two or more attributes are specified. When true, indicates that colors for overlapping dots will blend. For example, in a feature where a high density of blue dots exist on top of a high density of red dots, some of the dots may appear as purple dots if this property is true. When false only one color will be favored over the others in rendering.

Blend enabled Blend disabled
dot-density-blend dot-density-no-blend
Default Value:true
dotSize Number
Since: ArcGIS Maps SDK for JavaScript 4.23

Defines the size of the dots in points.

Default Value:1
Example
renderer.dotSize = 0.5;
dotValue Number

Defines the initial dot value used for visualizing density. If a referenceScale is provided, this value indicates the value of each dot at the view.scale matching the value in referenceScale. If referenceScale is set, the dot value will be recalculated depending on the view scale. Note the value of dotValue will remain constant even in this scenario. The variable dot value as displayed in the legend is recalculated using calculateDotValue(). If a referenceScale is not provided, the value specified in this property will apply to dots at all scales.

Examples
// Indicates that 1 dot = 100 people at any view scale
renderer.dotValue = 100;
renderer.legendOptions = {
  unit: "people"
};
// Indicates that 1 dot = 100 people only when the view's scale is 1:500,000
// And a new dot value is computed as the scale changes.
renderer.dotValue = 100;
renderer.legendOptions = {
  unit: "people"
};
renderer.referenceScale = 500000;
legendOptions Object

An object providing options for configuring the renderer in the Legend.

Property
unit String
optional

Indicates the unit of the data being visualized. this will display next to the dot value in the title of the Legend.

Example
// Legend will display: "1 dot = 50 cows"
renderer.dotValue = 50;
renderer.legendOptions = {
  unit: "cows"
};

The outline of the polygon. When not set, this renders using the default SimpleLineSymbol. It is good practice to explicitly set this for every DotDensityRenderer. Either remove the outline altogether, or set it to a very thin, transparent style so it doesn't distract from the dot density.

Examples
// removes the default outline from the renderer
renderer.outline = null;
// sets a thin, transparent outline to the renderer
renderer.outline = {
  color: [ 128,128,128, 0.2 ],
  width: 0.5
};
// disable the default outline
renderer.outline = null;
referenceScale Number

When defined, the renderer will recalculate the dot value linearly based on the change in the view's scale using the calculateDotValue() method. The rendering will maintain the density of points as drawn at the provided scale across various scales. However, the dot value will change as the user zooms in or out from the provided scale value, though the value of dotValue will remain constant.

When the computed dot value reaches 1, the dot value is no longer recalculated as the user zooms further in.

Example
// Indicates that 1 dot = 100 people only when the view's scale is 1:500,000
// And a new dot value is computed as the scale changes.
// When the scale is 1:250,000, the dot value will be 50.
renderer.dotValue = 100;
renderer.legendOptions = {
  unit: "people"
};
renderer.referenceScale = 500000;
seed Number

When set to a consistent value, dot placements will be preserved for the same scale given all parameters are the same in the renderer. By design, dot placement varies for the same feature across scales. If the user desires to see a different set of dot placements for a given scale, the developer may provide an alternate seed value to recalculate the random placement of dots.

Default Value:1
type Stringreadonly

The type of renderer.

For DotDensityRenderer the type is always "dot-density".

visualVariables VisualVariable[]autocast
Autocasts from Object[]

An array of Size Visual Variable objects. Only one ScaleDependentStops visual variable should be provided. This visual variable is used to vary the outline width based on the view.scale. See the snippet below for an example of this.

Example
renderer.visualVariables = [{
  type: "size",
  target: "outline",
  valueExpression: "$view.scale",
  stops: [
    { size: 1.5, value: 1881217},
    { size: 0.75, value: 5878804},
    { size: 0.375, value: 23515218},
    { size: 0, value: 47030436},
  ]
}];

Method Overview

Show inherited methods Hide inherited methods
Name Return Type Summary Class

Adds one or more handles which are to be tied to the lifecycle of the object.

more details
Accessor
Number

Calculates an updated dot value for the given scale for the cases where a referenceScale is provided.

more details
DotDensityRenderer
DotDensityRenderer

Creates a deep clone of the renderer.

more details
DotDensityRenderer
*

Creates a new instance of this class and initializes it with values from a JSON object generated from an ArcGIS product.

more details
Renderer
Boolean

Returns true if a named group of handles exist.

more details
Accessor

Removes a group of handles owned by the object.

more details
Accessor
Object

Converts an instance of this class to its ArcGIS portal JSON representation.

more details
Renderer

Method Details

addHandles(handleOrHandles, groupKey)inherited
Since: ArcGIS Maps SDK for JavaScript 4.25

Adds one or more handles which are to be tied to the lifecycle of the object. The handles will be removed when the object is destroyed.

// Manually manage handles
const handle = reactiveUtils.when(
  () => !view.updating,
  () => {
    wkidSelect.disabled = false;
  },
  { once: true }
);

// Handle gets removed when the object is destroyed.
this.addHandles(handle);
Parameters
handleOrHandles WatchHandle|WatchHandle[]

Handles marked for removal once the object is destroyed.

groupKey *
optional

Key identifying the group to which the handles should be added. All the handles in the group can later be removed with Accessor.removeHandles(). If no key is provided the handles are added to a default group.

calculateDotValue(scale){Number}

Calculates an updated dot value for the given scale for the cases where a referenceScale is provided. This allows the Legend to update the dot value as the user zooms in or out in the view.

Parameter
scale Number

The view scale at which to calculate a new dot value.

Returns
Type Description
Number The dot value used to render dots based on the given view scale.

Creates a deep clone of the renderer.

Returns
Type Description
DotDensityRenderer A deep clone of the object that invoked this method.
Example
// Creates a deep clone of the first layer's renderer
let renderer = view.map.layers.getItemAt(0).renderer.clone();
fromJSON(json){*}static

Creates a new instance of this class and initializes it with values from a JSON object generated from an ArcGIS product. The object passed into the input json parameter often comes from a response to a query operation in the REST API or a toJSON() method from another ArcGIS product. See the Using fromJSON() topic in the Guide for details and examples of when and how to use this function.

Parameter
json Object

A JSON representation of the instance in the ArcGIS format. See the ArcGIS REST API documentation for examples of the structure of various input JSON objects.

Returns
Type Description
* Returns a new instance of this class.
hasHandles(groupKey){Boolean}inherited
Since: ArcGIS Maps SDK for JavaScript 4.25

Returns true if a named group of handles exist.

Parameter
groupKey *
optional

A group key.

Returns
Type Description
Boolean Returns true if a named group of handles exist.
Example
// Remove a named group of handles if they exist.
if (obj.hasHandles("watch-view-updates")) {
  obj.removeHandles("watch-view-updates");
}
removeHandles(groupKey)inherited
Since: ArcGIS Maps SDK for JavaScript 4.25

Removes a group of handles owned by the object.

Parameter
groupKey *
optional

A group key or an array or collection of group keys to remove.

Example
obj.removeHandles(); // removes handles from default group

obj.removeHandles("handle-group");
obj.removeHandles("other-handle-group");
toJSON(){Object}inherited

Converts an instance of this class to its ArcGIS portal JSON representation. See the Using fromJSON() guide topic for more information.

Returns
Type Description
Object The ArcGIS portal JSON representation of an instance of this class.

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