silverstrata
In employment density terms, an airport is not terribly land-efficient.
Courtesy of Wikipedia entry on EGLL (many other sources available)
The airport sustains 76,600 jobs directly and around 116,000 indirectly in the immediate area, and this, together with the large number of global corporations with offices close to the airport, makes Heathrow a modern aerotropolis which contributes an estimated 2.7% to London's total GVA.
... on a site that covers 12.14 square kilometres (4.69 sq mi).
No one has yet counted how many other companies rely on being in the Heathrow Corridor for increased local employment.
So, that all looks pretty efficient to me.
Not to mention getting 69,433,230 passengers and 480,906 aircraft movements per year through that space.
Your witness ...