The March of the Adipose occurred in London.
The Adipose pill was given to overweight humans by Matron Cofelia (under the alias Miss Foster). The Adipose were produced from a kilogram of fat from those who had been taking the Adipose diet pills. Matron Cofelia activated her signal to induce the birth of the Adipose babies.
They marched along the streets of London towards the ship, though a couple were accidentally hit by a taxi when it tried to skid to a halt. The machine producing them was deactivated by the Tenth Doctor using two Adipose Industries pendants, but ten thousand Adipose had already been born. The Adipose walked to Adipose Industries HQ, where Miss Foster was waiting. Soon after, the Adiposian nursery ship descended and used levitation beams to lift the Adipose to the ship.
Once the Adipose babies had been brought onto the nursery ship, the Adiposian First Family deactivated the levitation beam carrying Matron Cofelia to the ship. They had realised that, as an accomplice to their criminal actions (interfering in a primitive planet, banned by the Shadow Proclamation), she was a liability which had to be removed. Matron Cofelia fell to her death. They then left Earth. (TV: Partners in Crime)
In a parallel world, the March of the Adipose occurred in America instead of the UK, because Britain was closed off from the rest of the world following the destruction of London and irradiation of Southern England. Sixty million Americans were killed when they were fully converted into Adipose children. (TV: Turn Left)