In 2025, Allegheny County could have a population of more than 1.3 million, reversing decades of steady decline. But it also likely will keep losing population in its older core communities, as suburban housing developments continue to grow on the county's outskirts.

That, at least, is the tentative projection of Allegheny Places, a project aiming to create the county's first comprehensive plan, a blueprint for future land use.

Planning officials have spent a year compiling information on the county's development trends. Now they want the public to help them imagine a different future.

Tomorrow, officials are hosting public workshops at 4 p.m. and 6:30 p.m. in the sixth floor lecture hall of Robert Morris University's Downtown building, 600 Fifth Ave. Participants will have a chance to voice their priorities for the county.

"The trend is not the plan. We can do better than that," said Joseph Bucovetsky, a lead planner with McCormick Taylor, a consultant for Allegheny Places.

Allegheny County is one of the last of Pennsylvania's 67 counties to develop a comprehensive land-use guide, which state agencies often use as a means for evaluating funding requests.

"If the county has a plan, it instills confidence in people. It makes it that much more attractive for investment," said Lynn Heckman, assistant director for planning in the county's economic development department.

The county officially launched its project in March of last year, with a budget of $2.5 million to $3 million. Since then, the planning team has collected more than 6,000 public surveys, held dozens of meetings with local municipal officials, and compiled detailed maps.

The team created a Web site, www.alleghenyplaces.com, that has been encouraging residents to answer a simple question: "What's your favorite place in Allegheny County?"

So far, the top pick has been PNC Park.

A draft of the comprehensive plan could be ready by the end of the year. County Chief Executive Dan Onorato and County Council must approve a final version.

First, however, officials need to keep gathering public input.

"What we're trying to do with this plan is find out what people want," Mr. Bucovetsky said. "Then we'll create more of it."

His firm, working with researchers at the University of Pittsburgh, compiled the "2025 Trend Scenario."

To illustrate those trends, Mr. Bucovetsky uses a county map covered by small squares, each representing a type of land use. Yellow squares, or residential development, cluster in the north and southwest, near Pittsburgh International Airport. Blue squares, or areas of widespread demolition, cover parts of the city of Pittsburgh and the Mon Valley.

During tomorrow's workshops, participants will move those squares as they consider a range of alternatives for the county, including rehabilitating existing communities, focusing on riverfront development, or building housing near major employment centers and public transportation hubs.

Some of those ideas aren't new. Mr. Onorato, since taking office more than two years ago, has pushed for development opportunities next to the airport and on unused industrial sites that line the rivers.

But the comprehensive plan gives the county a chance to coordinate those efforts. A final version likely will encompass a mixture of options.

Many of the county's 130 municipalities already have their own guides for land use, and the Allegheny Places planning team is trying to harmonize its work with existing plans.

Some, however, are out of date and likely will have to be updated when the county plan is finished.

Allegheny Places will gather more public input during a series of outreach meetings over the summer, and County Council will conduct hearings when it receives the draft plan later this year.