Meet the man who's transforming New York City's skyline

Architect Ismael Leyva has designed 65 buildings in New York City - enough to fill several city blocks - and he's got 12 more on the way.

After nearly 20 years of work in New York, Leyva is one of the city's most prominent residential architects, and he's left an indelible mark on the skyline. His firm, Ismael Leyva Architects, was involved in the massive Time Warner Center development in Lincoln Center, worked on the restoration of lower Manhattan's Battery Maritime Building, and is currently helping to design a residential tower at Hudson Yards, the biggest private development project the US has ever seen.

That expertise gives him a unique perspective about the future of the city. And there are several big issues he believes New York will have to tackle in the years to come.

First, he says, crowded cities like New York should focus on constructing buildings that have more than one function. That will help combat the inevitable congestion that comes with a growing population.

"The development of mixed use buildings, where retail, offices, hotels and residences are combined in one structure, or in a cluster of buildings - that's the dream, or it's going to be the dream." he explains. "Mixed-use buildings minimize travel distances, because people tend to concentrate in certain areas rather than spread, which is what has caused the problem of traffic."

Leyva is quick to note that he doesn't get to decide whether a building can be mixed-use - he is always subject to zoning regulations and other factors in his designs, and he gets hired to carry out a client's vision.

That's especially true when it comes to high-end condo buildings. Leyva has designed quite a number of them, and though he says he considers every project to be his baby, the quantity of luxury units on the market is concerning to him (as it is for many New Yorkers).

"I've seen in the past two or three years, they want to be the tallest and the most luxurious," Leyva says of the city's upscale condo towers. "And there's a limit of how many units you can build in those conditions. Affordable housing is important for the city, and it will continue improving the economy, I think."

Leyva says the city's real estate market is now saturated with luxury apartments. And the data backs him up - the New York Times reported in March that the number of sales in which buyers paid $5,000 per square foot peaked two years ago.

"The supply of high-end residences in some areas of the city has to be absorbed, and I think it's going to take a while," Leyva says.

But perhaps his biggest concern for New York - and other cities around the world - is the impact of rising land prices. From 2009 to 2014, average Manhattan land prices (south of 96th Street) jumped 53%, according to The Real Deal. Affordable housing and other forward-thinking construction projects can't proceed if lots are too expensive.

"The price of land I think is going to stop or slow development, because it's not affordable for the developers to develop sites - they are out of reach. That is a challenge for us architects because the amount of work is going to diminish," he says.

And since cities are expected to hold two-thirds of the world's population by 2050, the problem doesn't seem like it will go away on its own.

"I think it has to be adjusted somehow. Somebody has to be aware of that," Leyva says. "Things are not moving - they have to come down somehow for things to move, for the benefit of everybody, because then progress continues."

For the moment, though, Leyva's firm doesn't seem to lack for business. He is part of a team designing a 43-story luxury tower that broke ground in June at 45 Park Place, near Ground Zero. And the firm has been chosen to design an 11-story condo building next to the famous Katz's Deli.

Despite his concerns about the price of land - and the fact that he's now 64 years old - Leyva wants to keep adding to the New York City's skyline.

"I hope to continue contributing to the development of the city," he says, "providing buildings that are aesthetically pleasing, efficient spaces for people to enjoy."