RICHMOND - Every time Sen. Mark Herring casts a vote on the floor of the Virginia Senate, he has an unsettling thought: His vote should really count at least one and a half times.

Since his district in eastern Loudoun County was drawn a decade ago, so many newcomers have moved to its growing subdivisions that it has 100,000 more people than it would if the state's population was divided evenly among the 40 Senate districts.

Put another way, Herring's constituents in Loudoun now get only two-thirds of the say over what goes on in the Senate as residents in Lynchburg or Harrisonburg or Chesapeake, where growth has been slower.

But that's about to change.

On Thursday, the U.S. Census Bureau will deliver to Virginia the neighborhood population data from the 2010 census that is needed for the state to start its once-a-decade process of redrawing the lines of state legislative and congressional districts.

The General Assembly will use the data during a special redistricting legislative session in April, a highly political tussle in which partisanship and incumbency are bound to be important factors.

But one mathematical certainty is that the new maps will reflect a power shift in Virginia from south to north - and especially to Washington's outer suburbs, the epicenter of the state's economic vibrancy in the past decade.

In a state that sometimes feels like two culturally distinct worlds, Northern Virginians hope redistricting will give them the voting power to convince the rest of Virginia to take their concerns more seriously.

"We're going to have more representatives in the legislature who are in tune with issues that are important to suburban voters, more nuts-and-bolts governance issues," said Herring, a Democrat who has lived in Loudoun since the 1970s.

A decade of rocket-fast growth seeping outward from Washington has meant more than just new people in Northern Virginia. It's meant that more of the state now considers itself part of Northern Virginia.

Culpeper, Stafford, Spotsylvania - all these counties have seen a rapid influx of residents who feel more kinship to those who live to their north in Fairfax and Prince William than to the rest of the state.

Meanwhile, the state's old manufacturing towns and agricultural communities in Southside and Southwest Virginia have been shrinking as jobs are lost and young residents move to find employment.

Preliminary population estimates delivered annually have shown legislators the demographic contours. But this week's census report is expected to show with granular specificity just how much of a behemoth Northern Virginia has become. It also will provide neighborhood-level information about the state's racial and ethnic makeup.

"This is the real starting point," said Del. S. Chris Jones (R-Suffolk), who led redistricting for Republicans in the House of Delegates 10 years ago and will be heavily involved in the process again. "Once they arrive, you know it's not where you think the growth might have been over the last decade - but where the growth actually was."

Virginia will be one of the first places to receive its census report because it is one of only four states that will hold state elections in November.

It is also one of nine states that, under the 1965 Voting Rights Act, must submit new district plans for approval to the U.S. Justice Department to ensure they do not dilute the power of black voters.

"We've got a clock ticking," said Del. Robert G. Marshall (R), whose rapidly growing district in Prince William County may have to be cut nearly in half. "We can't procrastinate for too long for partisan advantage."

The process must be completed by a divided legislature where Democrats control the Senate and Republicans hold the House of Delegates.

Among the many issues that could trip up the process is timing.

In 2000, the General Assembly returned to Richmond in the summer to draw lines for congressional districts. This year, some Republicans, hoping to win control of the state Senate in November, may push to delay drawing congressional lines, which don't need to be drawn until the 2012 elections.

Democrats would oppose any delay, and Gov. Robert F. McDonnell (R) said Monday that he too believes the lawmakers should complete the process this year.

Aiding the legislature will be several Virginia universities, which are organizing a contest challenging students to use special computer software to come up with fair, logical maps without regard to party or protecting longtime incumbents.

The General Assembly also will receive input from a bipartisan commission formed by McDonnell. The commission held its first meeting Monday.

Legislative Democrats who have pushed for years to change the law to allow a bipartisan commission, rather than the legislature, to draw lines have called the panel a half-measure, since it will only provide informal advice the General Assembly is under no obligation to accept.

But opening the commission's meeting Monday, McDonnell said the body was embarking on a "historic task" to try to boost citizen input and guide a divided assembly to a fairer process.

"After you hear from me today, you will not hear from me again," McDonnell told the group. "I will not dictate or direct your work. Nor would I expect the legislature to be dictating or directing your work in any way. . . . This is, in fact, meant to be an independent panel."

Greater power for Northern Virginia in the legislature could affect the state's road funding formula. The region sends significant revenue to other parts of the state, despite the area's crushing traffic congestion.

A changed dynamic also could result in new attention to how the state funds education, distributing dollars from the wealthy northern districts to others that struggle to support their schools.

But leaders in both parties say Northern Virginia's growth does not provide either side a guaranteed advantage in coming elections.

While the region's core of Arlington, Alexandria and eastern Fairfax reliably vote for Democrats, the outer suburbs have swung back and forth between the parties in recent years, largely creating Virginia's reputation as an unpredictable state electorally.

Herring's district, for instance, backed President Obama in 2008 but a year later supported McDonnell for governor.

"It's the Willie Sutton theory," said Del. Robert H. Brink (D-Arlington). "That's where the people are. . . . And it's a question of who addresses the needs of those areas better."