The designation Historic Borderland covers the mainland areas Sundeved, Broagerland and the royal city Gråsten.
With a measurement of approx. 175 km2 the area represents about 1/3 of the municipality Sønderborg Kommune, which also includes the island Als.
Sønderborg Kommune has nearly 74,600 citizens of which the 24,500 is living on the mainland. The largest city of the Historical Borderland is Gråsten, with a population of approx. 4,200 people.
The area is connected by land to the neighbour municipality Aabenraa Kommune and surrounded by the two sounds Als Fjord and Als Sund towards the island Als as well as the bay Vemmingbund and the inlet border Flensborg Fjord towards Germany.
The landscape is extremely varied with ridges surrounding the city Gråsten land inwards and of the terrain model it becomes very clear, why the Danes decided to entrench themselves at Dybbøl Banke during the war of 1864. From the same model the Germans placement of cannons at Gammelmark also becomes logical, both places make out good strategic points for shooting at and defending Sønderborg city and the island Als.
The small inlet lagoon Nybøl Nor is a very special phenomenon of national, geological interest. The lagoon is 6.5 km2 an approx. 8 metres deep. It was made by a huge lump of ice in a glacial lake, connected to the inlet Flensborg Fjord by the narrow passage Egernssund. The melting time of the huge ice lump took extremely long which lead to deposits of the finest stone-free clay around the ice lump, on what later on became the banks of Nybøl Nor. Naturally the deposits where noticed and they became the foundation for an important industry of the area - brick works!