London City / City of London

[dan101smith]

So the City is the square mile, fine. However, what is considered to be "London City", as in which parts make up what is included when counting the population of London to rank the size of the city vs other cities in the UK?

The population of the City of London is something like 12,000 I believe, whereas the population of London City is considered to be more like 12 million.