Tver Oblast (Tverskaya oblast; Tverin alue) is a federal subject of Russia (an oblast). Its administrative center is the city of Tver. From 1935 to 1990, it was known as Kalinin Oblast (Кали́нинская о́бласть). Population: Tver Oblast is a region of lakes, such as Seliger and Brosno. Much of the remaining area is occupied by the Valdai Hills, where the Volga, the Western Dvina, and the Dnieper have their source. Tver Oblast is one of the tourist regions of Russia with a modern tourist infrastructure. There are also many historic towns: Torzhok, Toropets, Zubtsov, Kashin, Vyshny Volochyok, and Kalyazin. The oldest of these is Rzhev, primarily known for the Battles of Rzhev in World War II. Staritsa was the seat of the last appanage principality in Russia. Ostashkov is a major tourist center. Tver Oblast is located in the west of the middle part of the East European Plain. It stretches for 260 km from north to south and 450 km from west to east. The area borders Yaroslavl Oblast in the east, Vologda Oblast in the northeast, Novgorod Oblast in the northwest and north, Moscow in the southeast, Smolensk Oblast in the southwest, and Pskov Oblast in the west. The area of Tver Oblast is 84201 km2, the 38th of 85 subjects. This is 0.49% of the territory of Russia. It is the largest territory (by area) of the Central Federal District. Tver Oblast as a whole is characterized by flat terrain with alternating lowlands and highlands due to its location in the East European Plain. In the western part of the province, occupying about one-third of its area is Valdai Hills, with elevations of 200–300 m above sea level. It is surrounded by depressions, lowlands have a height of 100–150 m highest point of the area has a height of 347 m, is located on a hill Tsninsky (The top of the Valdai). The low point (61 m) - the extreme north-west area of the river's edge Kunya (Кунья) on the border with the Novgorod Oblast. Minerals discovered and developed in the Tver Oblast are mainly deposits of ancient seas, lakes and swamps, and partly a consequence of glaciers (clastic rocks).