qgis – Point Clustering and Legend in QGIS

clusteringlegendpointqgis

I am using the point cluster symbology in QGIS and have defined the size of each point based on the cluster size using @cluster_size in the size assistant.

It looks great on my map, but I cannot figure out how to add the size symbology for the variable to my legend in the map composer to create a map for a presentation/publication.

Best Answer

It's not possible to directly display data-defined symbol sizes in a legend. Here's a workaround.

Duplicate the point layer (Layer panel > right click on layer name > Duplicate layer).

Change symbology of the duplicate layer to "graduated" and for method choose "size."

Choose any numerical field for column.
Change the "Size from" starting value to 1mm, and the final value to the maximum number of points in a cluster.
Change the number of classes to the maximum number of points in a cluster (same as final size value).
Click "Classify."
Change the legend text as desired, eg "1 point," "2 points" etc.

The style settings for the duplicate layer look like this:

Turn off the duplicate layer so you don't see it on the map.

Use the duplicate layer in the print composer legend. The legend looks like this:

You can use the controls under legend items to

Change the way the layer name is displayed: highlight the layer name, click the pencil icon, type in the name of the original layer.
Delete the name of the field from the legend: highlight the field name, click the red minus sign button.

Related Solutions

[GIS] Leaflet Marker-Cluster JSONP GeoServer

To do that you can use the Leaflet.markercluster plug-in here https://github.com/Leaflet/Leaflet.markercluster. After adding it to your project, you have to define a marker cluster group:

var markers = L.markerClusterGroup();

Then, you should first add the markers to this cluster group and after that you have to add the group to the map:

markers.addLayer(a_group_of_markers);
map.addLayer(markers);

In your code you load the markers with Ajax and then you add them to the map, so the most straight way will be this:

var markers = L.markerClusterGroup();
var ajax = $.ajax({
    url : URL,
    dataType : 'jsonp',
    jsonpCallback : 'getJson',
    success : function (response) {
       WFSLayer = L.geoJson(response, {
            style: function (feature) {
                return {
                    stroke: false,
                    fillColor: 'FFFFFF',
                    fillOpacity: 0
                };
            },
            onEachFeature: function (feature, layer) {
                popupOptions = {maxWidth: 600};
                layer.bindPopup('<h4>'+feature.properties.url+'</h4><br>'+feature.properties.title
                    ,popupOptions);
            }
        }).addTo(markers.addTo(map));
    }
});

[GIS] QGIS 3.0 point cluster renderer, is it possible to control rendering order (z-order)

It seems as though the point cluster implementation does not allow for this natively.

Consider the point cluster renderer - it essentially analyzes and clusters point data at render time, creating a new pseudo layer. This layer is not accessible to the user. One cannot query a clustered point. One cannot field calculate a @cluster_size attribute.

The point cluster renderer does inherit render order from the source using Control feature rendering order (QgsFeatureRequest::OrderByClause) leaving open the possibility of some clever workaround using attributes and expressions, however certain ordering schemes are not guaranteed to be consistent.

As an example, consider a point layer with rendering ordered ascending by a "Latitude" attribute. The more northerly points are rendered atop more southerly points. The point cluster renderer does not have a "Latitude" attribute for its new features, though it will inherit some semblance of that order from the source. There can be instances when a more southerly cluster renders atop a more northerly cluster, because of the order of the original points.

Best Answer

Related Solutions

[GIS] Leaflet Marker-Cluster JSONP GeoServer

[GIS] QGIS 3.0 point cluster renderer, is it possible to control rendering order (z-order)

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