A very large population of Karachi comes in from interior Sindh, Punjab, KPK, Baluchistan and Azad Kashmir; they retain their residency status in their native cities and are not counted in Karachi even though they live in Karachi and utilize the resources and civic infrastructure of Karachi.
Who in their right mind can deny the population of Karachi to be under 30 million? Karachi is atleast 2x-2.5x Lahore and if Lahore is around 15 Million then Karachi has to be around 30-35 Million!
However, we all know why the marriage of convenience where people living their entire lives in Karachi are counted in their own respective cities......and what a disservice they are doing to the city which is feeding and keep them.