UPDATE: I have increased the number of points to trigger this feature from 100 to 500.
Publishing a map with hundreds or even thousands of markers can be problematic. Your maps may look like they are drowning in a sea of markers. Yesterday we rolled out a new feature that will help publishers with this problem.
Maps containing over 300 points with no groups assigned will have marker clustering enabled. This feature is thanks to the Google Maps Utility library. Below is an example.
Please post feedback on this feature here. I am still trying to sort out when is the appropriate time to have this feature turn on. I would rather not have to make it a toggle as I am interested in keeping things as simple as possible from an end user standpoint.