Color-printed German map of East Prussia, with extensive manuscript additions in a Soviet hand noting the troop movements during the East Prussia Offensive and encirclement of Konigsberg. The Red Army movements are shown in red pencil, Wehrmacht positions are shown in blue pencil.
The Soviet Union was producing many maps during the late stages of the war, but Red Army soldiers still frequently used captured German maps when recording troop movements and planning offensives.
The map was made after the encirclement of Georg-Hans Reinhardt's Army Group Centre, but before the closing of the Konigsberg Encirclement and the Heiligenbeil Cauldron (both of which can be seen forming on this map). The frontlines shown date the map to early-to-mid January 1945.
The map was apparently updated over time, as there are frontlines and pockets further east that are shown melting away in succession.
The East Prussian Offensive
Wikipedia gives the following summary of the East Prussian Offensive:
The East Prussian Offensive was a strategic offensive by the Soviet Red Army against the German Wehrmacht on the Eastern Front (World War II). It lasted from 13 January to 25 April 1945, though some German units did not surrender until 9 May. The Battle of Königsberg was a major part of the offensive, which ended in victory for the Red Army.
The East Prussian Offensive is known to German historians as the Second East Prussian Offensive. The First East Prussian Offensive (also known as the Gumbinnen Operation), took place from 16–27 October 1944, and was carried out by the 3rd Belorussian Front under General I.D. Chernyakhovsky as part of the Memel Offensive of the 1st Baltic Front. The Soviet forces took heavy casualties while penetrating 30–60 km (19–37 mi) into east-northern part of Poland, and the offensive was postponed until greater reserves could be gathered.