Each marker indicates one project. Most sites have one technique associated with them. By clicking on a map marker this will open a summary for that case study with a hyperlink to the PDF's.
Google automatically clusters sites close to each other on the map. Each cluster that has more than one marker (site) shows a count of the number of markers inside the cluster; otherwise a single marker is shown. Click on the cluster icon (number) to zoom in to a level where you can view the individual sites. Clustering changes dynamically depending on the zoom level.