Alexandria is an independent city in the Commonwealth of Virginia. As of the 2000 census, the city had a total population of 128,283. Located along the Western bank of the Potomac River, Alexandria is approximately 6 miles (9.6 kilometres) 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 Defence. Others include the Institute for Defence Analyses and the Centre 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 trade associations, charities, and non-profit organizations including the national headquarters of groups such as Catholic Charities, United Way, and 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 centre of Alexandria is known as Old Town. With its concentration of high-end boutiques, fine restaurants, antique shops and theatres, it is a major draw for tourists and those seeking nightlife. Like Old Town, many Alexandria neighbourhoods are compact, walkable, high-income suburbs of Washington D.C. It is the seventh largest and highest income independent city in Virginia. A 2005 assessed-value study of homes and condominiums found that over 40 percent were in the highest bracket, worth $556,000 or more.