For an Australian client I have developed an interactive map where they are able to see their Financial Planners & Accountants. Because there are a lot of employers that need to be displayed on the map, some clustering is practical. I have decided to use D3js and marker clustering, these are markers that aggregate the datapoints for a certain area. When a users zooms in the markers will fall apart in smaller markers until the marker has size 1. The number inside the markers tells the number of datapoints (employees).