From The Matrix wiki
Machine City
The Machine City is the central hub of machine civilisation located on the surface of the Earth, serving as the seat of power for the Deus Ex Machina.
The Machine City, often referred to as Zero One, is an expansive, highly industrialised metropolis located in the desolate ruins of the real world. Following the scorched earth tactics of humanity, the machines established this central hub to maintain the infrastructure required to power the Matrix and oversee the harvesting of human bio-electricity. It is a sprawling complex of dark metal, intricate circuitry, and towering spires that stand in stark contrast to the underground human refuge of Zion.
Significance
The city serves as the ultimate destination for Neo during the final events of the human-machine war. It is here that he encounters the Deus Ex Machina, the collective consciousness or primary interface of the machine hierarchy. The location represents the heart of the machine empire, acting as the nexus where critical negotiations regarding the survival of humanity and the stability of the Matrix are conducted.