 The Finnish strategy was dictated by geography . The frontier with the Soviet Union was more than 1 @,@ 000 km ( 620 mi ) long but was mostly impassable except along a handful of unpaved roads . In pre @-@ war calculations , the Finnish General Staff , which had established its wartime headquarters at <unk> , estimated seven Soviet divisions on the Isthmus and no more than five along the whole border north of Lake Ladoga . In that case , the manpower ratio would favour the attacker by three to one . The true ratio was much higher ; for example , 12 Soviet divisions were deployed to the north of Lake Ladoga . 
