Northern Ontario is a geographic and administrative region of the Canadian province of Ontario. The geographic region lies north of Lake Huron (including Georgian Bay), the French River, Lake Nipissing, and the Mattawa River, while the administrative region has several boundaries further south that vary according to federal and provincial government policies and requirements. The geographic region (which for census purposes, includes a part of Nipissing District that lies south of the Mattawa River) has a land area of 802,000 km² (310,000 mi²) and constitutes 87 per cent of the land area of Ontario, although it contains only about six per cent of the population. Most of Northern Ontario is situated on the Canadian Shield, a vast rocky plateau. The climate is characterized by extremes of temperature, extremely cold in winter and hot in summer.