The Office of Management and Budget delineates a metro area as one or more counties associated with at least one urban core of at least 50,000 people. It includes adjacent counties that have commuting ties to the urban center.

Typically, metropolitan areas that add the most people are also among the most populous. This is due to a higher potential for change that can alter the population, such as births, deaths and migration — both domestic and international.

Yet, some metro areas that gained a lot of people are not among the most populous.

Phoenix-Mesa-Scottsdale, Ariz.; Seattle-Tacoma-Bellevue, Wash.; Austin-Round Rock, Texas; and Orlando-Kissimmee-Sanford, Fla., were among the 10 largest metros by numeric growth, but not among the 10 most populous in 2018, ranking third, seventh, ninth and tenth, respectively.