Hi everyone, first time/long time. I understand what led to the erection of the wall, but the specifics will typically end at "well, Berlin and Germany was split based on territories invaded by the Soviets, and by the Western Allies". As a result, I just always assumed that the wall was based on the final positions of the Soviet army the moment Germany capitulated, but since Berlin, and Germany as a whole was only formally split a few years later, I'm wondering who drew "the line in the sand" and why that specific path was chosen. If you walk along the remnants of the wall, you'll notice that it zig zags through streets, neighbourhoods, wooded area, with little rhyme or reason (at least from the POV of someone who only knows modern day Berlin). There aren't really the natural border markers you'd typically see like a river, or forest or anything that would mark an obvious demarcation between the east and west.
Anyways, tl;dr: how was the precise location of the Berlin Wall decided?
The postwar zones of occupation covering Greater Berlin, which later hardened into East and West Berlin, were agreed by the Allies in September 1944 based on the city's municipal districts, as established in 1938. The original document lists the districts.
The occupation zones of Germany as a whole, and the division of Berlin into four occupation zones, was decided and planned during and just after the war. The larger zones did roughly parallel the position of the invading armies, but were not completely determined by that (a number of other considerations were involved). Rather, the actual positions of the armies merely provided a logical starting point. For example, the Allies actually penetrated much further into eastern Germany than the agreed borders between the zones, and that territory was later evacuated and placed under Soviet control. Alternately, the Western Allies never reached Berlin, but were still granted occupation zones there by the same agreements, even though it was well within the Soviet Zone/East Germany.
The actual criteria for the specific borders were many and complicated. One good example is the role logistics and strategy played. If you look at the maps of the zones, for instance, you'll see that the US had a small enclave at Bremerhaven, well within the British zone. This is because the Americans wanted to have their own port for supply purposes, even though their zone was otherwise entirely inland. The western Allies were also assigned certain air and land transport corridors to service their zones in Berlin. Basically, the process was "how do we divide Germany in four, considering absolutely every possible factor affecting the interests of the Allies and Soviets, and maybe the Germans if we have the time or inclination to do so."