Alexandria is an independent city in the Commonwealth of Virginia. Located along the Western bank of the Potomac River, Alexandria is approximately 6 miles (9.6 kilometers) south of downtown Washington, D.C. Like the rest of Northern Virginia, as well as central Maryland, modern Alexandria has been shaped by its proximity to the nation's capital. It is largely populated by professionals working in the federal civil service, the U.S. military, or for one of the many private companies which contract to provide services to the federal government. The latter are known locally as beltway bandits, after the Capital Beltway, an interstate highway that circles Washington, D.C. One of Alexandria's largest employers is the U.S. Department of Defense. Others include the Institute for Defense Analyses and the Center for Naval Analyses. In 2005, the United States Patent and Trademark Office moved 7,100 employees from 18 separate buildings in nearby Crystal City into a new headquarters complex in the city. Alexandria is home to numerous associations, charities, and non-profit organizations including the national headquarters of groups such as the Salvation Army. In 2005, Alexandria became one of the first cities of its size to offer free wireless internet access to some of its residents and visitors. The historic center of Alexandria is known as Old Town. It is a major draw for tourists and those seeking nightlife. Like Old Town, many Alexandria neighborhoods are high-income suburbs of Washington D.C. A 2005 assessed-value study of homes and condominiums found that over 40 percent were in the highest bracket, worth $556,000 or more.