The sectors were inside Berlin.
Germany’s large occupation areas were called zones. Berlin’s separately administered parts were called sectors. These two terms help distinguish the country-wide division from the special administration of a single city.
The Allied command authority, with representatives of the four powers, handled joint matters. In later developments, the American, British and French sectors formed West Berlin; the Soviet sector was referred to as East Berlin.
The other three answers
Being occupied is not the same as having joint four-sector administration.
Munich
American troops entered Munich in 1945. However, the division of a city among all four powers sought here concerned Berlin.
Dresden
Dresden was occupied by Soviet forces and was the seat of the Soviet military administration for Saxony. It was not the four-sector city sought here.
Frankfurt/Oder
Frankfurt an der Oder is not the city with this special joint four-power administration. The combination of four city sectors and four occupation powers belongs to Berlin.
The sector boundaries preceded the Berlin Wall.
The post-war division must not be equated with the construction of the Wall in 1961. Sectors and political division came first; the later Wall made the separation visible and enforced it through physical barriers and violence.
Berlin’s location in the Soviet-controlled east of Germany did not make the whole city an ordinary part of the Soviet occupation zone. The four-power arrangement explains why Western powers also had their own sectors there.
Four powers in Berlin · Berlin State Heritage Office ↗Germany: four zones. Berlin: four sectors.
The combination of “city” and “four sectors” points to Berlin.
Three words for this question
- die Viersektorenstadtfour-sector city
- A city divided into four separately administered sectors.
- die Kommandanturcommand headquarters / authority
- Here: the four powers’ joint military administrative body in Berlin.
- die Spaltungdivision / split
- The separation of something previously forming a whole.