This map uses size of the font to depict which area has more persons with the same surnames. An example would be Murphy which is typically from South West Ireland. My family's lineage is from the Murphy's in the East in county Wicklow.
The Goode-Homolosine projection is an interesting projection as it is a compromised projection that preserves the relative shape of the continents. It appears to distort both shape and area. It is almost as if you peeled the world the same way you would an orange if it was all one piece.