Höggom was pretty much where Sundsvall is today.
Also, about Svealand and Uppland. As it is today Uppland is a part of Svealand. Back then Uppland didn't exist as a region but was divided into several smaller provinces, at least about AD 1000 further back, no one's really sure. Further more the area around Uppsala was the center of Svealand so having another part called Svealand is a bit strange.