Boston is the capital and largest city of the Commonwealth of Massachusetts, and is one of the oldest cities in the United States. The largest city in New England, Boston is considered the economic and cultural center of the region and is sometimes regarded as the unofficial "Capital of New England". Boston city proper had a 2008 estimated population of 620,535, making it the twenty-first largest in the country. Boston is also the anchor of a substantially larger metropolitan area called Greater Boston, home to 4.5 million people and the tenth-largest metropolitan area in the country. Greater Boston as a commuting region includes six Massachusetts counties, Essex, Middlesex, Norfolk, Suffolk, Plymouth, and Worcester, all of Rhode Island and parts of New Hampshire; it is home to 7.5 million people, making it the fifth-largest Combined Statistical Area in the United States. With many colleges and universities within the city and surrounding area, Boston is a center of higher education and a center for medicine. The city's economy is also based on research, electronics, engineering, finance, and technology—principally biotechnology. Boston ranks first in the country in jobs per square mile ahead of New York City and Washington, D.C. The city has been experiencing gentrification and has one of the highest costs of living in the United States, and it remains high on world livability rankings