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MGLHeatmapStyleLayer

@interface MGLHeatmapStyleLayer : MGLVectorStyleLayer

An MGLHeatmapStyleLayer is a style layer that renders a heatmap.

A heatmap visualizes the spatial distribution of a large, dense set of point data, using color to avoid cluttering the map with individual points at low zoom levels. The points are weighted by an attribute you specify. Use a heatmap style layer in conjunction with point or point collection features. These features can come from vector tiles loaded by an MGLVectorTileSource object, or they can be MGLPointAnnotation, MGLPointFeature, MGLPointCollection, or MGLPointCollectionFeature instances in an MGLShapeSource or MGLComputedShapeSource object.

Consider accompanying a heatmap style layer with an MGLCircleStyleLayer or MGLSymbolStyleLayer at high zoom levels. If you are unsure whether the point data in an MGLShapeSource is dense enough to warrant a heatmap, you can alternatively cluster the source using the MGLShapeSourceOptionClustered option and render the data using an MGLCircleStyleLayer or MGLSymbolStyleLayer.

You can access an existing heatmap style layer using the -[MGLStyle layerWithIdentifier:] method if you know its identifier; otherwise, find it using the MGLStyle.layers property. You can also create a new heatmap style layer and add it to the style using a method such as -[MGLStyle addLayer:].

Example

let layer = MGLHeatmapStyleLayer(identifier: "earthquake-heat", source: earthquakes)
layer.heatmapWeight = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:(magnitude, 'linear', nil, %@)",
                               [0: 0,
                                6: 1])
layer.heatmapIntensity = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)",
                                  [0: 1,
                                   9: 3])
mapView.style?.addLayer(layer)

-initWithIdentifier:source:

Returns a heatmap style layer initialized with an identifier and source.

After initializing and configuring the style layer, add it to a map view’s style using the -[MGLStyle addLayer:] or -[MGLStyle insertLayer:belowLayer:] method.

Declaration

Objective-C

- (nonnull instancetype)initWithIdentifier:(nonnull NSString *)identifier
                                source:(nonnull MGLSource *)source;

Swift

init(identifier: String, source: MGLSource)

Parameters

identifier

A string that uniquely identifies the source in the style to which it is added.

source

The source from which to obtain the data to style. If the source has not yet been added to the current style, the behavior is undefined.

Return Value

An initialized foreground style layer.

Accessing the Paint Attributes

heatmapColor

The color of each screen point based on its density value in a heatmap. This property is normally set to an interpolation or step expression with the $heatmapDensity value as its input.

The default value of this property is an expression that evaluates to a rainbow color scale from blue to red. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

  • Constant UIColor values
  • Predefined functions, including mathematical and string operators
  • Conditional expressions
  • Variable assignments and references to assigned variables
  • Interpolation and step functions applied to the $heatmapDensity variable

This property does not support applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *heatmapColor;

Swift

var heatmapColor: NSExpression! { get set }

heatmapIntensity

Similar to heatmapWeight but controls the intensity of the heatmap globally. Primarily used for adjusting the heatmap based on zoom level.

The default value of this property is an expression that evaluates to the float 1. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

  • Constant numeric values no less than 0
  • Predefined functions, including mathematical and string operators
  • Conditional expressions
  • Variable assignments and references to assigned variables
  • Interpolation and step functions applied to the $zoomLevel variable

This property does not support applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *heatmapIntensity;

Swift

var heatmapIntensity: NSExpression! { get set }

heatmapIntensityTransition

The transition affecting any changes to this layer’s heatmapIntensity property.

This property corresponds to the heatmap-intensity-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition heatmapIntensityTransition;

Swift

var heatmapIntensityTransition: MGLTransition { get set }

heatmapOpacity

The global opacity at which the heatmap layer will be drawn.

The default value of this property is an expression that evaluates to the float 1. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

  • Constant numeric values between 0 and 1 inclusive
  • Predefined functions, including mathematical and string operators
  • Conditional expressions
  • Variable assignments and references to assigned variables
  • Interpolation and step functions applied to the $zoomLevel variable

This property does not support applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *heatmapOpacity;

Swift

var heatmapOpacity: NSExpression! { get set }

heatmapOpacityTransition

The transition affecting any changes to this layer’s heatmapOpacity property.

This property corresponds to the heatmap-opacity-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition heatmapOpacityTransition;

Swift

var heatmapOpacityTransition: MGLTransition { get set }

heatmapRadius

Radius of influence of one heatmap point in points. Increasing the value makes the heatmap smoother, but less detailed.

This property is measured in points.

The default value of this property is an expression that evaluates to the float 30. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

  • Constant numeric values no less than 1
  • Predefined functions, including mathematical and string operators
  • Conditional expressions
  • Variable assignments and references to assigned variables
  • Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *heatmapRadius;

Swift

var heatmapRadius: NSExpression! { get set }

heatmapRadiusTransition

The transition affecting any changes to this layer’s heatmapRadius property.

This property corresponds to the heatmap-radius-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition heatmapRadiusTransition;

Swift

var heatmapRadiusTransition: MGLTransition { get set }

heatmapWeight

A measure of how much an individual point contributes to the heatmap. A value of 10 would be equivalent to having 10 points of weight 1 in the same spot. Especially useful when combined with clustering.

The default value of this property is an expression that evaluates to the float 1. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

  • Constant numeric values no less than 0
  • Predefined functions, including mathematical and string operators
  • Conditional expressions
  • Variable assignments and references to assigned variables
  • Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *heatmapWeight;

Swift

var heatmapWeight: NSExpression! { get set }