---
title: annotationForCluster
framework: mapkitjs
role: symbol
role_heading: Instance Property
path: mapkitjs/map/annotationforcluster
---

# annotationForCluster

A delegate method for modifying an annotation that represents a group of annotations that the framework combines into a cluster.

## Declaration

```data
get annotationForCluster():
    | ((clusterAnnotation: ClusterAnnotation) => Annotation | undefined)
    | null;
set annotationForCluster(
    value:
        | ((clusterAnnotation: ClusterAnnotation) => Annotation | undefined)
        | null,
);
```

## Parameters

- `clusterAnnotation`: An annotation that represents a group of annotations that MapKit JS combines into a cluster.

## Discussion

Discussion MapKit JS invokes this delegate method when it creates a cluster annotation, or when a member annotation within the cluster changes. You can return any of the following: The same cluster annotation with its properties, such as title or subtitle, modified. A new annotation, such as an image annotation, to represent the cluster. No return value. If you don’t return an annotation, MapKit JS uses the default annotation. You don’t need to return a default annotation even if you modify it (as the following code example shows for the cities cluster); the map displays the modifications. The following example creates annotation clusters for cities and parks: map.addAnnotations(cities.map(city =>     new mapkit.MarkerAnnotation(city.coordinate, {         title: city.name,         subtitle: city.population,         glyphImage: city.landmarkImage,         displayPriority: Math.max(city.population / 10000, 1000),         clusteringIdentifier: "city"     }) ));

map.addAnnotations(parks.map(park =>     new mapkit.ImageAnnotation(park.coordinate, {         title: park.name,         url: { 1: park.image },         displayPriority: 250,         clusteringIdentifier: "park"     }) ));

map.annotationForCluster = function(clusterAnnotation) {     if (clusterAnnotation.clusteringIdentifier === "city") {         clusterAnnotation.title = "Cities";         clusterAnnotation.subtitle = clusterAnnotation.memberAnnotations             .reduce((total, clusterAnnotation) => total + clusterAnnotation.population, 0);     } else if (clusterAnnotation.clusteringIdentifier === "park") {         return new mapkit.ImageAnnotation(clusterAnnotation.coordinate, {             title: "Parks",             url: { 1: "tree.png" }         });     } }; For more information, see Clustering annotations.

## See Also

### Annotating the map

- [annotations](mapkitjs/map/annotations.md)
- [selectedAnnotation](mapkitjs/map/selectedannotation.md)
- [annotationsInMapRect(mapRect)](mapkitjs/map/annotationsinmaprect.md)
- [addAnnotation(annotation)](mapkitjs/map/addannotation.md)
- [addAnnotations(annotations)](mapkitjs/map/addannotations.md)
- [removeAnnotation(annotation)](mapkitjs/map/removeannotation.md)
- [removeAnnotations(annotations)](mapkitjs/map/removeannotations.md)