In Scandanavia...a family takes the first name of the father and adds son or datter to his name and that becomes the name of the child. So, Erlandsen means son of Erland. ie:
Gudmund Hansen would be the father of Arne Gudmundsen
or Anne Gudmundsdatter. Gudmund's father first name would be Hans. They also use a farm name. So if Gudmund's family lived on the farm Haakerud...he would be known as Gudmund Hansen Haakerud.