Check your version
This tutorial covers a topic in Drupal 7 which may or may not be the version you're using. We're keeping this tutorial online as a courtesy to users of Drupal 7, but we consider it archived.
Sprout Video
In this lesson, we'll add the Markercluster library and contributed Drupal module which will transform the behavior the Leaflet map markers to display clusters instead of individual markers.
Additional resources
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Changing the Base Map Layer