The archipelago at the Swedish Baltic coast belonging to the landscapes Södermanland och Östergötland consists of many thousands of islands today. However, about 10 000 years ago, the first islands broke the sea surface due to the land uplift. Despite of the very exteme maritime environment at that time there exist archaeological remains from the mesolitical period from the first visitors. Since that time the maritime landscape has been used for several reasons, such as providing food, establishing industry, defence and trade. In the viking and medieval age the activity was high in the archipelago. This could only be possible with a safe journey between the islands with help from local fishermen who were the experts of the archipelago and severed as pilots as they know the safe routes and the placenamnes. The intention of this essay is to test if the phenomena called "name user circle" is present along the Swedish Baltic Sea coast of Södermanland and Östergötland. This means that a limitid group of people, geographically located, used the same placenamn for, in this case the placenamne Hamnskär (harbour islet). The frequensy and locality of Hamnskär will be studied as well as the historical och archaeological materiel. Other questions will be answered, such as common factors for Hamnskär, who used them, what were they used for, where did the users come from and who gave the islands their placenamnes. The result of the test is that ten Hamnskär have been found relatively frequently along the tested coast, except outside Södertörns coast, a part of Södermanland. Five "Bodskär" ("hut-islet") were located here. To go fishing in the outer archipelago you need a boat, a harbour and a hut, the use of these islets is the same. Archaeological materiel exits on some islets. The islets were used for fishing and for self-sufficiency. As the fishing was very income-generating a lot of people came to fish, even the Crown and burghers. Some other placenames have been found along the tested coast, Björkskär 18 and Alskär 26. The conclusion is that Hamnskär is a part of a local name user circle.