City planning was one thing when you had a blank space on the map - say, a forested Manhattan Island or a nice piece of undeveloped land rising gently from the natural harbor formed where the Patapsco River meets the Chesapeake Bay.
Then, you could paint an urban picture without interference, laying out roads in a neat grid pattern and putting parks and schools and houses and shops and churches and cemeteries pretty much where you wanted.
It is quite a different challenge a couple of centuries later, when the roads are already there (too many well-potholed) and the once-pristine grid contains a confusing melange of development and despair, economic prosperity and grinding poverty, booming construction and depressing dilapidation.
That's what faces Baltimore planners as they set about drawing up the city's first master plan in more than a third of a century.
The question is, can lines on a map and well-meaning words have any impact on reality?
A half century or more ago, cities were in charge, the places with the best shopping, the best schools, the best infrastructure, where everyone, public and private, wanted to spend money. Draw some lines on a map, and a Robert Moses-type highway would soon follow.
And if you go back to the last time Baltimore created a master plan - 1971 - you find a time when the nation was concerned about the decline of the cities and was pumping money into redevelopment. Draw some lines on a map, and you might get Harborplace.
The question in 2006 - when cities have lost political power and their place in the funding pecking order - is: Does it make any difference what lines get drawn on a master plan map?
"I think it does," says Matt Crenson, a political scientist at the Johns Hopkins University who specializes in urban affairs.
But he recognizes that now the marketplace has a much greater say in the fate of cities and their neighborhoods than planners do.
"If they don't try to go against the forces of the market, but work with the forces of the market, then they can help magnify what is good about the city and minimize what is bad," Crenson says.
John Iceland, a sociologist at the University of Maryland, College Park, agrees.
"It's true that market forces sometimes overwhelm other forces, but that does not mean that planners cannot do anything, that they should not bother," he says.
Sandra Newman, director of Johns Hopkins' Institute for Policy Studies, says that no matter how the master plan ultimately affects reality, drawing it up is a good exercise for any city to go through.
"It is a very useful tool to take stock of where you are," she says, because it brings together in a systematic way the plethora of useful - but often unorganized - data that are out there.
"It allows you to say where you are now - and where you want to be - in something other than a smoke-and-mirrors way," Newman says.
"Now you are actually looking at hard evidence and information," she says. "In a best-case scenario, using that in a very analytic and creative way, it can give you a look into the future."
But who knows what that future will actually look like?
Think of what must have been envisioned in 1971 when Baltimore's last master plan was drawn up. Charles Center was in place and had brought a modicum of respectability back to the center city, but downtown was still deserted at night - unless the Baltimore Bullets had a basketball game at the Civic Center. That was a long time ago.
It was also the year William Donald Schaefer became mayor, bringing with him a coterie of inventive urban-redevelopment minds. It might have been possible to imagine clearing the Inner Harbor of the dilapidated market buildings that cut off the water from the city, but could anyone have dreamed of the success of the aquarium?
How about Canton, then still an industrial center, turning into a yuppie haven? Or arty shops moving onto The Avenue in Hampden? Go figure.
"The best approach is to be flexible," Newman says. "As you get new information and new trends, adjust to that while staying true to your general principles."
Certainly, plans can achieve things beyond placing parks and schools. Newman says she has recently been focusing on Baltimore's low-end rental market, an important part of the city's housing puzzle.
"One thing I try to point out is that we actually do have quite a lot of money coming into Baltimore, $95 million in the last five years for housing alone," she says. "It is very, very difficult to find out exactly what we were spending it on."
The planning process can help sort that out. "Ninety-five million is not exactly chicken feed," Newman says. "We have to make sure we are making wise decisions."
Iceland says planners can help ensure the economic heterogeneity of neighborhoods by setting aside certain sites for affordable housing. "More mixed-income populations are often accompanied by less racial and ethnic segregation," he says.
Crenson points out that one fundamental lesson learned since the 1971 plan is, "the key to urban economic development is residential growth.
"Some cities that pursued that strategy from the very beginning, like St. Paul, Minnesota, decided - instead of waterfront malls or industrial parks - to focus on residential retention," he says. "Once you get people downtown, businesses follow."
But there are elements outside of planners' control, particularly good schools. Without those, you have a hole in the urban doughnut - the only families with children left in the city are those too poor to move or rich enough to afford private education.
"Unless you create a school system that gives an acceptable option for these people, you will only get them in the city for a limited part of their life cycle," Crenson says.