At the start of 2006, 15 casinos were within about 600 miles of Atlantic City. Today, that number has nearly tripled to 39 casinos, including six that opened in 2012.

The crowded scene directly affected Atlantic City, which previously had seen gambling revenue grow consistently year-over-year. But in 2006, at the height of that growth, five new casinos — Parx and Mohegan Sun at Pocono Downs in Pennsylvania, and Empire City, Tioga Downs and Vernon Downs in New York — opened within about 300 miles of Atlantic City.

Atlantic City’s gambling revenue began trending downward, plunging by more than 35 percent. While the weak economy was one factor, competition was another, particularly from Pennsylvania, which now has 11 casinos, and New York, with the addition of Empire State Raceway in Yonkers and Aqueduct in Queens, analysts say.

Some industry observers, however, say damage to Atlantic City’s gambling revenue by Pennsylvania and New York has reached its maximum and that new properties expected to open will have less of an impact, because they are farther away.

“Most of the impact on Atlantic City has been felt,” said Michael Soll, a Florida-based president of The Innovation Group, a consulting firm that conducted casino research for Massachusetts before the state authorized the start of gambling.

“People go to the closest possible product they are looking for,” he said.

There are more casinos expected to open in the Northeast and Mid-Atlantic regions, although the pace is expected to slow in the coming years.

New York is considering expanding gambling beyond Indian casinos and slot parlors. Gov. Andrew Cuomo has said he wants the first three to be upstate. Pennsylvania expects to issue another license in Philadelphia, and Massachusetts is in the midst of awarding as many as three resort casino licenses and one for a slots parlor. Farther away, Ohio, which had three casinos last year, has two more under construction.

But the projected growth is still less than the explosive growth seen over the past six years, industry analysts say.

“We’re through the big wave of gambling expansion in the Northeast,” said Clyde Barrow, director of the University of Massachusetts Dartmouth Center for Policy Analysis and author of the New England Casino Gaming Update, an annual report on the regional casino industry. “We’ve hit a point of stability and equilibrium.”

Atlantic City wasn’t the only market affected by the expansion wave. Pennsylvanians used to represent a sizable group of patrons for Connecticut’s two casinos, Foxwoods and Mohegan Sun, Barrow said. But starting six years ago, when Pennsylvania and New York casinos started opening, those customers almost stopped coming to Connecticut casinos, he said.

They numbered so few that researchers, who would annually survey the license plates of patrons’ cars in the parking lots of the two Connecticut facilities, dropped reporting Pennsylvania as its own line item.

Barrow said that while Northeast casinos compete for gamblers who live within driving distance, he sees an untapped market in the Southeast, where casinos aren’t as prevalent.

Attracting those gamblers, however, would require an expansion of air service into South Jersey. That has proved problematic at Atlantic City International Airport in Egg Harbor Township, where Spirit Airlines is the only commercial carrier. Some casinos have organized charter flights for some of their patrons, and private jet service is available.

Jeff Guaracino, strategy officer for the Atlantic City Alliance, a marketing nonprofit funded by the casino industry, said that while officials have discussed marketing to air travelers, they have decided to direct the first phase of their $25 million annual advertising budget toward visitors who live within a few hours’ drive from Atlantic City.

“The opportunity to continually market to a quarter of the country’s population, which lives a five-hour drive from Atlantic City, is an important thing to do,” he said.

The advertising campaign also specifically avoids making references to casinos in Atlantic City, instead focusing on the shopping, entertainment, dining, nightlife, spas and other attractions.

“The point of our campaign has been to appeal to those leisure visitors who have not really considered Atlantic City as a place for them,” Guaracino said. “That really does point to what we are looking to do, which is to get people here who have various interests.”

Atlantic City is working to diversify its offerings, particularly in nongambling attractions and midweek and special events.

Caesars Entertainment has plans in place to build a new conference center next to Harrah’s Resort. Resorts Casino Hotel has begun incorporating a new Margaritaville theme, including a LandShark Bar & Grill under construction on the beach and plans for a Margaritaville Cafe, 5 O’Clock Somewhere bar and renovated casino floor space inside.

Some of that work is starting to be reflected in revenue derived from nongambling activities as seen through increased collection of luxury taxes, parking fees and hotel taxes, said Israel Posner, executive director of the Lloyd Levenson Institute at Richard Stockton College. The institute is set to begin regularly publishing a report that will detail strides Atlantic City has made in generating money for those funds.

“What we’re seeing is that the city is growing as a tourist attraction, with more interest in nongaming amenities,” Posner said. “The future of Atlantic City will be as a broad-scale entertainment resort.”

Depending on the outcome of a federal lawsuit involving New Jersey and the professional sports leagues and NCAA, the start of sports betting also could be a boon for Atlantic City, Posner said. Sports betting would be an amenity that would draw visitors during the February Super Bowl and March Madness.

“It fills in a period where Atlantic City is particularly slow,” Posner said.

In the short term, Atlantic City is still working to overcome misconceptions some people have about the amount of damage Hurricane Sandy caused to the resort.

Guaracino said that in the days immediately after the storm, his agency funded a survey that found that 41 percent of people across the country wrongly believed that the city’s entire Boardwalk was destroyed, but only a short, dilapidated, rarely used portion was damaged. Officials said they have since conducted another survey and are reviewing the results to see whether a media blitz conducted late last year has succeeded at correcting those misconceptions.

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