These are visitors since 30 days ago, though the caption on the map appears stuck on “90 days”. I really was gathering stats over 90 days for some time, but that caused this widget to break once the 90-day total got past 10,000 hits. The minuscule dots represent places my visitors came from. Hover your mouse over them to get an approximate location.
This plugin was re-activated on December 23, 2014, so the numbers will be off for 90 days past that date.
Visitor Maps right now only gives basic stats. The map itself does not display for some reason.