Forty years ago, when Richard J. Daley was Chicago's mayor, urban planners and social scientists developed a premise of urban renewal that came to be called the "Emerald City" theory. Their prognostication was that the urban decay which then blighted parts of Chicago's Loop and adjacent areas to the south and west would be cured by a capitalist-inspired urban renewal in which affluent whites, wanting to live close to their jobs, would build or rehab housing which would push out impoverished blacks.

Like an emerald, which appears to glow from within, these observers believed that the influx of white residents into the inner city would precipitate an out-migration of blacks to elsewhere in the city, which would then precipitate an out-migration of outlying city whites to the suburbs, so that Chicago, by the early 2000s, would consist of three concentric rings extending off Lake Michigan.

First, a Lakefront, central city ring running from Rogers Park in the north to Hyde Park in the south and to Garfield Park in the west, would be populated primarily by affluent whites in new or rehabilitated high-priced housing. This will eventually occur, but not before 2015. A second ring stretching outward to Chicago's borders would be populated by blacks and other minorities residing in declining housing stock, and a third ring in the suburbs would be overwhelmingly white and would contain moderate-priced housing.

But the above hasn't occurred exactly to projections. Instead, the "Emerald City" theory became the "Leaking Tire" theory. While Chicago's core has been redeveloped, pushing blacks out of the Near West Side, the out-migration of the city's black residents has instead been to Cook County's western and southern suburbs, not into white areas on the city's fringe -- much like a tire that leaks from the wheel rim, not the tread.

The reasons for that are fivefold: High property values on the Northwest and Southwest sides made it impossible for poorer people to buy housing; a city requirement that city workers live in Chicago kept whites in; the election of Mayor Richard M. Daley in 1989 diminished the impetus behind "white flight"; an influx of Eastern European immigrants, primarily Poles, beginning in the late 1970s kept the Northwest Side largely white; and an even larger influx of Hispanic immigrants, primarily Mexicans, beginning in the mid-1980s blunted blacks' migration to the Southwest Side.

The Northwest Side, for example, has undergone major demographic and socioeconomic change over the past two decades, but only minimal racial change. It has become much more affluent. Property values are stunningly high, with relatively few houses to be found for less than $200,000 and with many in the range of $400,000 and up. It's much more ethnic, with high numbers of foreign-born residents. It's younger, with fewer retirees than in the 1980s. And it's more Hispanic, but only about 15 percent overall, especially in the Albany Park and Belmont-Central areas. And, most significantly, there are still relatively few blacks residing on the Northwest Side.

Which brings us to the "Starburst Theory," namely, that the Polish immigration into the Belmont-Central area, as it exploded outward, blocked black movement into the area from the West Side Austin area, and that the huge infusion of Mexicans into the Humboldt Park and Little Village areas, as they exploded outward, blocked black movement into those areas.

Chicago's boom of upscale housing has grown outward from the Loop, beginning with the West Loop and the University of Illinois/Medical Center area and then in the 1990s to the United Center (at Madison-Damen), and now encroaching westward along the Eisenhower Expressway to California. So, too, has the housing boom affected parts of the Northwest and Southwest sides. Here's how:

* Outlying areas: According to the 2000 census, which surveyed Chicago's 77 neighborhoods for affluence, three of the 10 with the highest household median income were on the Far Northwest Side: the Edison Park, Norwood Park and Sauganash-Edgebrook-Forest Glen areas. Four were along the Lakefront, extending from near North Michigan Avenue to Lakeview, and three were on the Far Southwest Side, in Ashburn, Beverly and Mount Greenwood.

In those areas, property values were the highest: Older, larger homes in the outlying areas are going for $400,000 and up, while Lakefront condos and single-family homes are going for $600,000 and up. As with a starburst, those values are expanding outward, as from the Far Northwest Side southeastward into Jefferson Park, Portage Park and Albany Park. Likewise, both values and white home buyers are expanding from the Lakefront and Wicker Park northwestward along Milwaukee Avenue and North Avenue into Logan Square and Humboldt Park.

Only on the Far Southwest Side is a siege mentality developing. Property values remain high, but whites are not spreading inward; instead, middle class blacks are buying in Mount Greenwood, and those whites who depart are generally moving out toward Orland Park and Tinley Park, and to Mokena and Frankfort in Will County.

* Polish and East European immigration: The once-huge concentration of Polish immigrants in the Belmont-Central area has substantially dispersed. According to a survey of local real estate agents, the preponderance of new home purchases in the area are by Hispanics. The Polish immigrants who arrived in America in the 1980s and 1990s, and who have accumulated some affluence, have long since moved out of Belmont-Central.

Many moved to moderately priced homes -- in the $200,000 to $275,000 range -- in Jefferson Park and Norwood Park, as well as in Niles, Skokie, Morton Grove and Des Plaines, but the last few years have been characterized by their mass infusion into near west suburbs like Elmwood Park, River Grove, Northlake, Franklin Park, Harwood Heights and Norridge. North Avenue seems to be a demarcation line: the Hispanic population is concentrated south of North Avenue, and in the area to the north is the increasing Polish-American and other ethnic population.

One starburst area on the Northwest Side is Portage Park, where older, spacious homes are selling for upwards of $375,000 and new townhouses along Milwaukee Avenue between Irving Park and Addison are listed for $500,000. At some point, in the next 20 years, the corridor between Wicker Park and Portage Park will be complete, and it will populated by upscale whites in pricey homes. Right now, dwellings in Wicker Park, at Milwaukee-Damen-North, are going for upwards of $750,000; just 15 years ago, Wicker Park was primarily Hispanic.

* Hispanic areas: With redevelopment proceeding at a breakneck pace in Wicker Park and points west, Hispanics who occupy rental units in Logan Square and Humboldt Park are being forced out. Where are they going?

The "Hispanic exodus corridors" for lower-income Hispanics are quite clear: into west suburban Melrose Park and Stone Park, or farther west into DuPage County, into Bensenville or Addison, or northwest into Des Plaines or Wheeling, or way north to Waukegan, or west to Aurora or West Chicago or Elgin. But for more affluent Hispanics, who seek housing and not rental units, the prime choices are Chicago's Northwest Side and Cicero.

With interest rates at all-time lows, it doesn't take much more than $900 a month to afford the mortgage on a $200,000 house. According to local real estate agents, the bulk of the new home buyers in the area around Belmont-Central and northward into Jefferson Park and Albany Park are Hispanics, many of whom have city jobs and the overwhelming majority of whom are of Mexican heritage.

The influx of immigrant Hispanics during the 1980s and 1990s and their settlement in both Logan Square and along the Stevenson Expressway acted as a geographic pincher on Chicago's West Side black population, as did the Polish influx into Belmont-Central and the white outburst from the Loop.

As a result, West Side blacks were squeezed, and they could only move westward, into Maywood, Bellwood, Forest Park and Broadview, or pull up stakes and move to the South Side. And that's what happened. As with a domino, many of the poorer West Side blacks moved to the Near South Side, along the Dan Ryan Expressway from Pershing to 79th Street, and this influx prompted many of the middle class South Side Chicago blacks in the area from 63rd Street southward to relocate to the south suburbs.

* Black exodus: Thirty years ago the entire crescent of south suburbs from Oak Lawn to Calumet City was predominantly white. Now, it's predominantly middle class black, as South Siders moved to the area in droves. Close-in suburbs such as Robbins and Phoenix are over 90 percent black, while farther south, Markham, Chicago Heights, South Holland, Homewood, Olympia Fields, Blue Island, Matteson and Flossmoor are majority black. But there is a line of demarcation: West of Harlem is solidly white. And a large proportion of the whites who moved out of the south suburbs have settled in Will County.

The bottom line: There is a growing black population in the area around Armitage and Narragansett, in the 36th Ward, but only a small percentage of black residents elsewhere on the Northwest Side. As long as Daley or some other white politician is mayor and schools are good, there will be a continuing economic starburst on the Northwest Side, with hefty property values soaring even higher.