Dick Garver of the Boston Redevelopment Authority explained that the rules, approved by the Federal Highway Administration, call for a public process for development of Big Dig land parcels. A consensus on uses, heights, density and other aspects needs to be agreed on before a request for proposals is issued. The BRA, Massachusetts Turnpike Authority, and the public all have a say in the process.

And so it begins on the 29,400-square-foot Blackstone block, located next to one of the two North End Greenway parks. "We are starting from scratch here," said Garver.

Well, not exactly. A consultant hired by the city is studying possible uses for the site - with special instructions to try to accommodate the pushcarts, Garver said. So, while discussion will go on concerning the upper floors of any future building, the subject of first-floor uses is off limits for the time being.

Frank Keefe, chief executive of the Boston Museum Project, was sitting in the back of the room. The museum, designated for one of the difficult-to-build-on ramp blocks of the Greenway nearby, now has its eye on the Blackstone block, as Garver acknowledged. There might be some other proposals too, after the request for proposals goes out - though any original thought of a hotel or housing there is pretty unlikely. The active pushcart business can make it unpleasant even now for people trying to sleep at the Millennium Bostonian Hotel on the corner.

For some fascinating glimpses of what the Blackstone block and that whole section of the city looked like before it was demolished in the early 1950s to make way for the elevated Central Artery, see Yanni Tsipis' fascinating book, "Boston's Central Artery," in the Images of America series published by Arcadia.

Tsipis, now of Colliers Meredith & Grew, was in the audience. He assists the Boston Public Market, the growers group that used to operate at Dewey Square, but now is shut out of that location because of the cost of the required police details. The Public Market may also someday have a presence on the Blackstone block.

Some residents at the meeting argued for low height or no height at all on the block, but the BRA's David Carlson explained that the city would probably look for something along the lines of the current zoning and the historical maximum of about 55 feet - and some variation, which is also depicted in those wonderful old '50s photos.

"The long-term intent is to build out the block as it was historically," said Carlson. An building much lower "is not likely to be economical for anybody except someone who doesn't have to be concerned with economics."

Down at the southern end of the Greenway block that the Boston Museum Project is assigned to, the one known as Parcel 12 that's too expensive to build on, near Christopher Columbus Park, is a lovely little rectangle of land of about a third of an acre. After a nasty public process, a local Armenian-American group has won the right to place a park, including sculpture and water feature, on the site.

Even people who have helped negotiate the wording that will go on a plaque on the site still can't tell us specifically what it will say, except that it will commemorate not only the Armenian Genocide of the early 20th Century but also, more broadly, the immigrant experience of many who came to Massachusetts and the United States for a better life.

The park, a gift to the city from the Armenian community, was designed by architect Donald Tellalian and is exquisite. It's been improved during the long and sometimes difficult public process, according to BRA officials, but unfortunately won't be constructed until sometime in 2009.

At least the gravel and chain-link fence that once cursed the site are now gone, replaced by an open lawn. A group of curious visitors being led on an informative tour organized by the nonprofit Boston by Foot (617.367.2345) enjoyed the openness on Aug. 21. More on that next time.