The city also agreed to pay the authority $200 million for unused development rights from the railyard on the east side of the avenue.

A 10,000-square-foot church on a site where a 100,000-square-foot tower could be constructed would have 90,000 square feet of unused development rights to sell.

Those unused development rights would almost certainly affect the future of surrounding blocks.

Almost 1.8 million square feet of unused development rights are attributable to Grand Central.

But the figure is probably nowhere near three million square feet of unused development rights on theater sites.

Exploiting unused development rights, or air rights, is another way to add value, the memo says.

The city is also offering to pay $200 million for 3.42 million square feet of unused development rights from the eastern yard.

All told, Rockefeller Center has about 2 million square feet of unused development rights.

There were unused development rights from the Saks store itself, which is smaller than it could have been under zoning rules.

By their nature, theaters are small in scale and therefore tend to have abundant unused development rights.