The result is quite interesting. The most common names seem to be dividing Sweden close to what used to be the old lands of Sweden. Eriksson is the most common name in Svealand. In Gothia, Johansson is the most common name in Westrogothia and Karlsson is the most common name in Ostrogothia. Near Stockholm (near the Karlsson-Eriksson border), Andersson is most common. In Scania and Blekinge that used to be Danish, Nilsson and Svensson are the most common names. In the island of Gotland the name Petterson is the most common.
Now we just have to figure out how the Westrogothian name Johansson became the most common name in the north of Sweden.