There are "büyükşehir belediyesi" (or greater municipalities) for large cities like İstanbul or İzmir and consist of an extra administrative layer run by an elected head mayor, who oversees a number of municipalities and mayors.
There are "büyükşehir belediyesi" (or greater municipality) for metropolises like İstanbul or İzmir. This consists of an extra administrative layer which is run by an elected head mayor, who oversees a number of municipalities and mayors.