ORLANDO, Fla. – Where someone lives makes a difference in whether or not that person has health insurance.

Census data released this week shows a vast geographic inequality in the uninsured that has been shaped by an area's state laws, population makeup and jobs. Residents in pockets of the Northeast and upper Midwest are many times more likely to have health insurance than residents of vast swaths of the Southwest.

"Depending on who you are and where you work, you can be very unlucky and not get covered," said Dr. Bruce Siegel, director of the Center for Health Care Quality at George Washington University. "It's a completely fragmented system."

Of the nation's 435 congressional districts, Texas districts topped the list with the highest percentage of uninsured residents, while the lowest percentage of the uninsured were in congressional districts in Massachusetts, which in 2006 legislated near-universal health insurance.

The extremes range from Democratic U.S. Rep. Gene Green's congressional district in Houston, where 40.1 percent of the population is uninsured, to Democratic Rep. Jim McGovern's district around Worcester, Mass., where only 3.4 percent of the population has no coverage.

McGovern's district is helped by having the University of Massachusetts Medical School and UMass Memorial Medical Center as two of the area's largest employers.

Green attributed the large numbers of uninsured in his inner-city district to low-paying jobs where employers don't provide insurance, and even if they do, employees often can't afford the high co-payments.

"We've been trying to hold a finger in the dike," Green said.

In between these extremes are the San Francisco congressional district of House Speaker Nancy Pelosi, where more than 11 percent of the residents are uninsured, and the South Carolina district of Republican U.S. Rep. Joe Wilson, where almost 15 percent of residents have no health insurance. Wilson gained fame for his outburst of "You lie!" during President Barack Obama's speech to Congress on health care reform.

The reasons for the geographic disparities boil down to state policies, types of jobs and demographics.

Eligibility for Medicaid, the federal health program for poor families managed by states, varies between states: Some are more generous than others. In Massachusetts' case, lawmakers mandated that virtually everyone in the state be insured or face steadily increasing fines, dropping the percentage of uninsured to 4.1 percent.

An Associated Press statistical analysis showed that a county's percentage of residents without health insurance was influenced by its percentage of Hispanics; the percentage of residents ages 20 to 24 and 60 to 64; and the percentage of residents working in farming, fishing, hunting, mining, construction, real estate, support positions such as secretary or janitor and hotel and food service workers.

Salaries matter too, as well as the presence of government and union jobs.

While more than 90 percent of the nation's highest-wage earners had access to health insurance, that was true for little more than a quarter of the nation's lowest wage-earners. Just under three-quarters of the nation's workers had access to health insurance, but the access rate jumped to 88 percent for government workers, according to the Bureau of Labor Statistics.

Construction workers in heavily unionized areas of the United States, such as the Northeast, Chicago and California, are more likely to have health coverage than in right-to-work states in the South and Southwest, said Jacob Hay, a spokesman for the Laborers' International Union of North America. Workers in right-to-work states can't be forced to join a union as a condition of employment.

Indeed, BLS data showed that 80 percent of union workers in private industry had health insurance benefits in 2006, while only 49 percent of nonunion workers did.

"A solution we would point to is that when workers are able to come together in a union, they're able to fight for better jobs, and part of that includes fighting for and negotiating health care benefits," Hay said.

The four states with the highest concentrations of the uninsured — Texas, Nevada, New Mexico and Florida — also have some of the nation's largest Hispanic populations.

"Much of the explanation lies in the kinds of jobs they have," said Jill Quadagno, a Florida State University sociology professor. "Fewer are in state employment compared to blacks and more are in agricultural employment, often migrant labor, which does not provide health insurance."

With the age groups, people between ages 20 and 24 may be least likely to have health insurance because they don't have jobs, have jobs that don't include health insurance or have aged-out of their parents' health insurance coverage.

Some people in the 60 to 64 age group may be making too much money to qualify for public insurance but they can't afford private insurance. Others may be early retirees whose company didn't provide health insurance in retirement but they're too young to qualify for Medicare, the federal program which provides health insurance for people age 65 and older, Siegel said.

Next to Massachusetts, the states with the least uninsured residents were Hawaii (6.7 percent), Minnesota (8.7 percent) and Connecticut (9 percent).

Behind Texas, the states with the largest percentage of uninsured residents were New Mexico (21.4 percent), Nevada (21.3 percent) and Florida (20.8 percent), where 41-year-old Tanya Cheaney lives.

When Cheaney lost her customer service job earlier this year at an Orlando cabinet maker, she not only lost her health insurance but her ability to pay for the $400-a-month in anti-seizure and blood pressure drugs she needs every day. She now faces the choice of going without the medication or putting off her car insurance payments so she can buy the drugs.

"We're going to have to rob Peter to Paul," Cheaney said.

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Associated Press writers Juan Lozano in Houston and Steve LeBlanc in Boston contributed to this report.