On television weather maps, thunderstorms stand out as bright, sharply defined clusters of intense energy.
A similar picture emerges on a new map of employment in the Washington area that documents a tremendous concentration of job growth in the region's outer suburbs over the past decade.
The reverse of that story, according to the analysis presented last week at a Brookings Institution conference on the region's economic future, is a shrinking job base in the District and slow growth in three of its oldest, closest suburban areas -- the close-in portions of Prince George's County and Bethesda-Chevy Chase and downtown Silver Spring in Montgomery County. The conference report is available on the Internet at www.brookings.edu.
This pattern of starkly uneven regional job growth highlights a division of the Washington area into "haves" and "have-nots," along a north-south axis, says the study's author, Myron Orfield, a Minneapolis-based urban analyst.
Roughly following a line along Interstate 95 and 16th Street through the District's center, this division shows the capital region's inability to remedy the consequences of segregation and poverty that go back several centuries.
In the here and now, the surging growth on the region's western and northern extremities, coupled with a stagnant economy on the region's east side, threatens to suck the economic vitality out of the older, inner suburbs, according to Orfield's analysis.
In preparing the map, Orfield's Metropolitan Area Research Corp. calculated how job growth in major employment centers compares with job growth throughout the region.
Over the past decade, seven job clusters in the region, including Manassas, Frederick, Laurel-Greenbelt and Springfield, grew twice as fast as the region's overall average. The number of jobs in three areas grew between five and seven times faster -- Dale City, Reston-Herndon and along Route 7 in eastern Loudoun County.
The growth champion was a bottle-shaped area including Dulles International Airport and Chantilly, where jobs increased at nearly 10 times the regional average.
The Washington area has reaped great dividends from this job growth, much of it led by technology companies that have given the region a new economic foundation not linked to federal employment. The expansion has attracted billions of dollars in investment, creating windfall stock gains for investors and a new entrepreneurial class.
But the growth's concentration on the region's perimeter has contributed to growing traffic congestion that could curtail the technology boom.
And in bypassing older commercial centers in the District and the Capital Beltway, the expansion is worsening the region's economic and racial divisions, Orfield argues.
Until now, the strongest response to the region's growth challenge has come from the area's technology business leaders and the Greater Washington Board of Trade. Operating as the Potomac Conference, this group hopes to mobilize public opinion behind a campaign for major transportation projects that have been stalled by the growth-no growth debate.
Brookings' entry into the fray puts the voice of an influential capital think tank behind a different agenda. Although the Brookings group is withholding recommendations for now, Orfield and his colleagues strongly favor moves to control growth; build more subsidized, affordable housing; and channel jobs into older, already developed parts of the region.
Neither strategy faces an easy road. Key political leaders were noticeably absent from the most recent Potomac Conference, where the transportation campaign was announced.
And when a moderator at last week's Brookings session asked for elected public officials in the audience to stand up and be recognized, Prince William Supervisor Mary K. Hill was the only one on her feet.
These ratings compare the increase in jobs within selected employment centers with the average job growth rate for the entire Washington region. An area with a 2.0 rating would have grown twice as fast as the region overall.
Crystal City, Alexandria, Bethesda, Chevy Chase, Silver Spring, Central Prince George's County
Metropolitan region index
Tysons Corner, Rockville, Rosslyn, Ballston1.30 to 1.74
Merrifield, Fairfax, Gaithersburg, Laurel, Greenbelt, Manassas
Reston, Herndon, Route 7, Loudoun, Dale City
SOURCES: Robert Charles Lesser & Co.; Washington Metropolitan Council of Governments