Megalopolis
Megalopolis (meg`ȧ*lop"o*lis) , noun
[New Latin, from Greek megalo`polis; me`gas, mega`lh, great + po`lis city.]
1.
A chief city; a very large city; a metropolis.
2.
A region in which the suburbs of several large cities merge to form one large predominantly urbanized area.
Also: Megapolis