People have spoken. Experts have weighed in. Varying interests have been balanced. Maps have been drawn.

Now, the redevelopment of the sprawling State Hospital property on Bull Street comes down to “density” — a small, bureaucratic word that holds all the pitfalls and all the profit.

To put it concisely, density — the number and height of housing, office and retail units that can pack a given tract of land — is everything.

And when the final Bull Street plan is unveiled at 7 tonight at the Columbia Metropolitan Convention Center, density will have shaped it all.

Density will decide the price the state will receive for the land.

Density will decide the profit for builders and developers.

Density will decide how much homes, town houses and condos cost.

Want to keep the trees? You affect the density. Want to save old buildings? You affect the density. Want dog parks and jogging trails? You affect the density.

“It’s the heart of it,” said Columbia financier Don Tomlin, who has been working behind the scenes to promote the development.

Tomlin has vowed not to invest in Bull Street so he can become an advocate for it.

“They will be working right up till the last minute on density,” he said.

The estimates on what a master developer would be willing to shell out for the 178-acre campus vary wildly, but insiders are talking in the $15 million to $20 million range.

Andres Duany, the Miami-based architect whose firm is redesigning the old asylum, knows the lower the selling price of the land, the more amenities he can include and the more striking the project can be.

“I guarantee that (the architects were) closeted for three days over the weekend running numbers, trying to meet their mandate,” Tomlin said. “You’ve got to have significant density or it’s not going to pay. And the first thing that dictates density is the price aspirations of the seller.”

The seller in this case is the state. More precisely, it’s the State Budget and Control Board, comprising:

• Gov. Mark Sanford

• Bobby Harrell, R-Charleston, chairman of the House Ways and Means Committee

• Hugh Leatherman, R-Florence, chairman of the Senate Finance Committee

• Grady Patterson, the state’s comptroller general, a Democrat

• Richard Eckstrom, the state’s treasurer, a Republican

The board will accept bids on the property after the city approves, and possibly tweaks, Duany’s development plan.

If the board remains true to form on land deals, it will be Sanford and Eckstrom holding out for a maximum sales price — which sets up a political bear trap for Duany.

The money goes to the state. But a well designed and successful project is hugely important to Mayor Bob Coble and the city.

Not a comfortable arrangement for an architect, and Duany is worried about the differing priorities.

“The difficulties may be political,” he said.

That was likely the topic of conversation when Duany hopped into Coble’s black SUV last Wednesday at breakfast and Sanford’s black sedan at lunch.

Publicly, Duany has played the density game close to his vest.

“I haven’t a clue about the density,” he said during last week’s series of input and planning sessions. “But I know the state wants maximum value. And I also know that this project has a responsibility to be excellent.”

Whether Duany, an architecture guru and pioneer of “new urbanism,” can pull it off will be determined, in large part, tonight.