Publix doesn’t build in a neighborhood without doing its homework. So the grocery chain’s confirmation this week that it plans to open a store in the Channel District is a pretty solid indicator that downtown Tampa has achieved the critical residential mass it has long sought.

For years now, grocers have looked around downtown Tampa and declined to build. Too many empty lots and too many commuters heading out of downtown at 5 p.m. to make a store work.

But the tide is turning now that thousands of apartment and condo units are either built, coming out of the ground or planned for the area in and around the Channel District.

A 38,000-square-foot grocery store may not seem like much, but it effectively turns the area into a neighborhood.

As the Tribune’s Jerome R. Stockfisch reports, the grocery store will be built in retail space at the Channel Club apartment project planned for the intersection of East Twiggs Street and Meridian Avenue.

The Channel Club is one of several substantial developments in the works that will contribute to a doubling of the residential units downtown from 6,000 to 12,000 in a few years. Lightning owner Jeff Vinik has embarked on a $2 billion redevelopment of 40 acres near the Amalie Arena that will include commercial and entertainment venues to go along with the residential component. And Port Tampa Bay in August unveiled an ambitious development plan for 45 acres in the Channel District that includes hotels, residential towers, a park and marina.

Opening a store in the Channel District means Publix will have two stores serving portions of downtown. An existing Publix at the edge of downtown, near neighborhoods on the west side of the Hillsborough River, will remain open.

The unprecedented residential growth spurt means added tax revenue for Tampa, and at least part of that money should be earmarked for a more modern streetcar system to help people get around town.

Several engineering firms have expressed an interest in studying how the existing streetcar system might be transformed from the little-used shuttle for tourists and conventioneers into a working transit system.

Preliminary estimates put the cost of such a transformation at $60 million, and no doubt a streetcar would have to be subsidized to some degree. But with the expanded downtown tax base, the project seems feasible and one that should become a priority for city officials. Visitors, workers and downtown residents will all benefit from a reliable system that can deliver people from one end of downtown to the other.

Downtown Tampa appeared headed for a renaissance in 2007. But the recession brought those plans to a screeching halt. Now that the construction cranes have returned to meet the pent-up demand, Mayor Bob Buckhorn’s relentless pursuit of a bustling downtown continues to make great strides.