The de Blasio administration kicked off the rezoning of Governors Island with the release of a key document today.

A notice posted by City Hall advertises the plan's first public hearing, which will take place next month as part of an environmental-review process. The rezoning aims to spur 4.5 million square feet of mixed-use development on the southern portion of the island. Officials hope it will attract some combination of tech and life-science firms, education institutions, dormitories and a convention center and hotel.

"This is a chance to have both great public open space and great culture but also use development to give more people exposure to this amazing place," Alicia Glen, deputy mayor for housing and economic development, said in an interview.

Governors Island is a 172-acre former military base nestled in New York Harbor that boasts views of Brooklyn, Lower Manhattan, New Jersey and the Statute of Liberty. The city took full control of the island in 2010 on the premise that the Trust for Governors Island would fund its own operating and maintenance costs. With that in mind, after completing a 43-acre park in 2016, the city is now turning to a pair of development sites carved out on the southern portion of the island. Revenue from that would be used for the new park's year-to-year costs.

The parcels are zoned for residential development, which is prohibited on the entire island by covenants with an exception for student housing. To address that contradiction, the rezoning would encourage relatively low-rise commercial properties with large floor plates, similar to the loft-style buildings popular in Midtown South and a few projects rising on the Brooklyn waterfront. Dorm or hotel buildings, on the other hand, would be allowed to rise to a height of around 300 feet.

"We don't want the zoning to be very prescriptive because we don't have an identified user," Glen said, explaining the need for flexibility.

The proposal will need to traverse the public review process, which is expected to culminate with a City Council vote in fall 2019. Should it pass, the trust and the city would entertain proposals from developers willing to finance and construct new buildings on property leased from the trust, potentially in combination with subsidies.

In preparation for workers coming to and from the island, the city has ordered a second ferry that together with the trust's existing vessel will offer trips as often as every 10 to 15 minutes from the Battery Maritime Building in Lower Manhattan. The de Blasio administration's East River ferry line also stops at the island during summer weekends and could increase its frequency.

However, even such expanded service would be insufficient to barge enough people to regularly fill 4.5 million square feet of development. Without adequate transportation capacity, developers won't build and the trust won't get the revenue it is projecting from the ground leases. That is why the city is looking for another way for people to get to and from the island.

As Crain's reported in the spring, the city's Economic Development Corp. is studying the possibility of a gondola between Lower Manhattan and Governors Island. Glen said officials could make the call about whether to pursue the idea as soon as next year, after the rezoning process. If the city were to move forward, an avalanche of permits would be needed from city, state and federal agencies to erect support structures in the harbor.

"Let's just say it's like a jurisdictional mosh pit," Glen said.

The trust, led by former Related Cos. executive Michael Samuelian, is also working to activate around 1 million square feet of landmarked military buildings at the north end of the island that are in various states of disrepair.