Narrower definitions may be based on other geographical factors such as climate and ecology. A broader definition would include the area north of the Alps. Countries which are central-western (such as Belgium), central (such as Austria) or central-eastern (such as Poland) are not usually considered part of either Northern or Southern Europe.
Historically, when Europe was dominated by the Roman Empire, everything not near the Mediterranean region was termed Northern Europe, including southern Germany, all of the Low Countries, and Austria. This meaning is still used today in some contexts, for example, discussions of the Northern Renaissance.
Northern Europe consists roughly of Fennoscandia, the peninsula of Jutland, the Baltic plain that lies to the east and the many islands that lie offshore from mainland Northern Europe, Greenland, and the main European continent.
The area is defined by the volcanic islands of the far northwest, notably Iceland and Jan Mayen, the mountainous western seaboard, extending from the mountainous sections of Great Britain and Ireland to the Scandinavian mountains peaking in Norway, the central north mountains and hills of Sweden (which are the foothills of the Scandinavian mountains) and the large eastern plain, which contains, Lithuania, Latvia, Estonia and Finland.
The region has a south west extreme of around 50 degrees north and a northern extreme of 81 degrees north. The entire region's climate is mildly affected by the Gulf Stream. From the west climates vary from maritime and maritime subarctic climates. In the north and central climates are generally subarctic or Arctic and to the east climates are mostly subarctic and temperate/continental.