Helicopters are not supposed to fly within 500 feet of tall structures in central London, he said.

CNN: London helicopter crash prompts safety questions

That was built when no one was used or understood tall structures, but it showed what could be done and just as importantly stretched the imagination.

CNN: Can wooden skyscrapers transform concrete jungles?

How about the city government designates a set of aesthetically valuable historic buildings and then lets the rest of the land be filled with tall modern structures to meet the demand for space?

FORBES: Underground Living is a Solution in Search of a Problem

Similarly located structures less than 45 metres tall may require a low-intensity light.

BBC: London helicopter crash: What are the rules for pilots?

Glass structures might work in New York, in the shadows of tall buildings, but how would they fare under direct California sun?

CNN: Mark Milian,