The Soviets controlled all of Berlin, and all of its suburbs in 1945. Why create this geographic oddity? Was Stalin trying to keep the USSR open to the west and have them interact?
/u/bigbadsaint and /u/hanrohan have previously answered Why did Stalin start the Berlin Blockade in 1948? which offers some background.
/u/kieslowski_fan explained why the Western Allies continued to have access to West Berlin after 1961. and compared the different occupations of Germany after 1945.