A Metropolitan Statistical Area must have at least one urbanized area of 50,000 or more inhabitants. It consists of no less than one county. There are 370 Metro Areas.
If specified criteria are met, a Metropolitan Statistical Area containing a single core with a population of 2.5 million or more may be subdivided to form smaller groupings of counties referred to as "Metropolitan Divisions." Eleven Metropolitan Statistical Areas (Boston, Chicago, Dallas, Detroit, Los Angeles, Miami, New York City, Philadelphia, San Francisco, Seattle, and Washington D.C.) have a total of 29 Metropolitan Divisions.
A Micropolitan Statistical Area must have at least one urban cluster of at least 10,000 but less than 50,000 population. It typically consists of one county. There are 565 Micro Areas - 71 of which include two counties or one county and a Virginia city, 18 of which include three counties, and two of which include four counties (the Paducah, KY-IL Micropolitan Statistical Area includes Massac County, IL; Ballard County, KY; Livingston County, KY; and McCracken County, KY while the Traverse City, MI Micropolitan Statistical Area includes Benzie County, Grand Traverse County, Kalkaska County, and Leelanau County).
Furthermore, there are 116 brand-new Combined Statistical Areas (CSA) which consist of adjacent metropolitan and micropolitan statistical areas. A CSA may comprise two or more Metro Areas, a Metro Area and a Micro Area, two or more Micro Areas, or multiple Metro and Micro Areas. They are not all huge population centers, by any stretch of the imagination. For example, the Paducah-Mayfield, KY-IL Combined Statistical Area simply consists of the Paducah Micro Area and Mayfield Micro Area.
The terms Consolidated Metropolitan Statistical Area and Primary Metropolitan Statistical Area are purely historic; they no longer exist.
The name of the CSA lists the most populous component area first. Thus, in a dramatic upset, the historic San Francisco-Oakland-San Jose, CA CMSA (Consolidated Metropolitan Statistical Area) has become the San Jose-San Francisco-Oakland, CA Combined Statistical Area. Ouch!
Let's take an example of how Metro areas and Micro areas come together. The Sacramento--Arden-Arcade--Roseville, CA Metropolitan Statistical Area consists of four California counties in the Sacramento area - El Dorado County (largest city South Lake Tahoe), Placer County (where the urban core of Roseville is located), Sacramento County (where the urban cores of Sacramento and Arden-Arcade are located), and Yolo County (largest city Davis).
However, the Sacramento--Arden-Arcade--Truckee, CA-NV Combined Statistical Area includes a new place name (Truckee) in the CSA name. The CSA includes three components two Micropolitan Areas to the east of Sacramento proper - the Gardnerville Ranchos, NV Micropolitan Statistical Area and the Truckee-Grass Valley, CA Micropolitan Statistical Area along with the Sacramento--Arden-Arcade--Roseville, CA Metro Area.
The Gardnerville Ranchos, NV Micropolitan Statistical Area is simply Douglas County, Nevada and the Truckee-Grass Valley, CA Micropolitan Statistical Area is simply Nevada County, CA. This brings up some interesting questions - 1) Why is Douglas County, Nevada (near the Nevada state capital of Carson City) part of the Sacramento CSA while closer Alpine or Amador Counties (neither are in a Micro or Metro area at all) are not? 2) Why then isn't Reno or Carson City (closer to Sacramento than Douglas County) part of the CSA? Reno and Carson City (two separate Metro Areas) aren't in a CSA at all. Strange indeed but this is what the OMB has given us to work with and enjoy.
For your enjoyment, all 116 CSA names are listed for you on page two of this article.
