TAMPA — In December, Jeff Vinik unveiled his $1 billion vision to transform 40 acres of downtown property into a vibrant waterfront district. He asked the public to help shape it.

Now it's time to ask the experts.

Vinik has hired two men considered among the best in the business: "new urbanists" Jeff Speck and David Dixon are city planners at the forefront of the movement to build walkable urban spaces for people to live and work in.

Speck's hiring leaked out last week and Dixon's was announced on Tuesday, when the mission for both also was made public. They will create the guidelines that builders will use to fulfill Vinik's "vision plan" of creating a vibrant and pedestrian-friendly space to unite the district and connect it to the water.

In short, they will design the ground floor of Vinik's urban redevelopment project.

"When a developer is trying to build a vision plan, you're still left with a lot of questions," Speck said. "A vision plan embodies peoples' hopes and aspirations for the project but doesn't give you the specificity you need in terms of:

"How many lanes on every street? How wide are the lanes? Where does the parking go? How tall are the buildings? Where exactly will people sit?"

Dixon and Speck will lead a team of architectural designers, residential and retail planners, and transportation and traffic engineers who will answer those questions.

"We need to give the architects that will be (designing) the individual buildings in the project a firm understanding of what their urban obligations are," Speck said.

But there's more to it than that. Most urban construction takes place in designated sites. Architects don't have to worry about also designing the surrounding areas.

What Vinik wants the two urban planners to do is something entirely different: create a new neighborhood and business district from scratch.

"When you're building an urban district, every building has to help each other create that public realm," Dixon said. "Public realms are not one size fits all. We're a very diverse society. This is a district that belongs to everybody."

Dixon, 67, will lead the master plan team. He's also the senior principal and urban design group leader for the urban design arm of Stantec, an international engineering firm. Dixon was named to Residential Architect magazine's hall of fame in 2012.

Speck, 51, will serve as consulting design leader. He has his own Washington D.C. firm, Speck & Associates LLC. He's also a vocal proponent of new urbanism — creating neighborhoods that are hospitable to pedestrians and offer a variety of employment and living options — as well as a vociferous critic of suburban sprawl and auto-dependency.

Vinik brought Speck on board after reading his book, Walkable City: How Downtown Can Save America, One Step at a Time. Vinik liked the book so much he bought copies for his entire staff.

Vinik called Speck over the winter holidays and asked him to come see his project. Speck was vacationing with his parents in Sarasota's Siesta Key and tried to beg off. But he'd already heard of Vinik's project, and couldn't say no to the former hedge fund star.

"I said — with a gulp, because it was Jeff Vinik — I'm sorry I don't have an opening in my calendar for a couple of months," Speck said. "But I happen to be in Tampa Bay. I guess I can stop by."

Speck signed up, and so did Dixon. The two know each other through their work as proponents of new urbanism. But this is their first project together.

They have four months to come up with a plan.

Vinik owns the leases to the Amalie Arena and Channelside Bay Plaza and he owns the Tampa Marriott Waterside Hotel & Marina outright. But he also owns about 25 acres of barren, blighted lots connecting those properties.

All of his holdings are within walking distance of the Tampa Convention Center, the Florida Aquarium, the Tampa Bay History Center, the Channel District neighborhood and a public waterfront park, Cotanchobee Fort Brooke Park.

Speck said that, taken together, the established properties and the empty lots are ripe with possibility:

"To find 40 acres of principally surface parking this close to downtown that already has anchors in place in the form of an arena, a museum, a convention center, an aquarium, a marketplace, and you still have all this empty space and the waterfront. What could have greater potential?"

Dixon said Vinik's project has the most promise of any current urban redevelopment effort he's seen.

"Nobody has 40 acres," he said.

Times researcher John Martin contributed to this report. Contact Jamal Thalji at thalji@tampabay.com or (813) 226-3404. Follow @jthalji.