Built with a merger here, a bonus there.

How Trump built a tower 310 feet taller than the United Nations is a story in its own right.

According to the Municipal Art Society, who are spearheading a citywide coalition to overhaul the old zoning laws, the answer has to do with a "zoning lot merger" along with a plaza bonus.

Here is the Municipal Art Society's breakdown:

Trump originally purchased a building lot of 20,083 SF. By law, the tower that he can build is ten times that size (or 200,830 feet). Shaping this tower into a narrow slab adds to its height while clearing a zone of empty space around the base of the building. In zoning terms, this empty space is called a "plaza."

The plaza earns Trump a "plaza bonus" that lets him build 20% larger. Trump then adds 40,166 SF to the tower.

While this is happening, Trump is negotiating with his neighbors. After cutting some deals, he merges his zoning lot with seven other lots that cover much of the block. These lots all have buildings on them though they are much smaller than the zoning allows. That difference -- between them and the new buildings that could be built there -- now belong to Trump as development rights. These rights give Trump much room to build.

By scooping up these rights, Trump places them on top of his own building, thereby adding 526,105 SF of floor space. What you now have is a 767,101 SF tower.

But remember that zoning has no ceiling limit. So Trump raises his tower even higher by pushing the ceiling heights to 20% above the average.

Even though the zoning resolution limits the floor space of a building on this site to ten times the size of it's lot, Trump's building will be more than thirty-eight times the area of its lot.

In the end, according to the Municipal Arts Society, you have an 856-foot tall building that should have been less than 250 feet tall.