The Geography of Southern Arizona
Do you know all the geographical regions in Southern Arizona? There are many and it is helpful to know specifically what they are. This article explores the geographic layers of Southern Arizona from the community level on up to the metropolitan area. Since Tucson is the largest place in the southern part of the state and is made up of multiple geographic layers, it works well as an example of the different geographic types found in Southern Arizona. Maps will be utilized throughout the article to explore the different layers of geography in Tucson and Southern Arizona. A glossary of geographic terms, most of which are based on U.S. Census Bureau definitions, is also included.
The first geography to define is Southern Arizona. Which part of the state are we referring to on the MAP Dashboard? The MAP defines Southern Arizona to include these counties: Cochise, Pima, Pinal, Greenlee, Graham, Santa Cruz, and Yuma. The Southern Arizona counties are highlighted in orange on Figure 1.
Figure 1: Southern Arizona Counties
There are three Metropolitan Statistical Areas (MSAs) in the Southern Arizona region: Sierra Vista-Douglas, Tucson, and Yuma. These cover the counties of Cochise, Pima, and Yuma, respectively. Metropolitan statistical areas are determined at the county level and contain an urbanized area with population of 50,000 or more. They can consist of more than one county if there is enough integration between the counties, and outside of Arizona, that is often the case. In Arizona, the only example of that is the Phoenix-Mesa-Chandler MSA, which contains both Maricopa and Pinal counties. While Pinal is part of the Phoenix-Mesa-Chandler MSA, the MAP considers it a part of the Southern Arizona region. There are also two micropolitan statistical areas in Southern Arizona: Nogales, which covers Santa Cruz County, and Safford, which includes Graham County. Micropolitan statistical areas contain an urban cluster with a population of at least 10,000 but less than 50,000.
Let’s look closer at the urbanized area geography. The Census Bureau developed the urbanized area concept in the 1950s to include suburbs and other areas of concentrated population around cities and to differentiate between urban and rural. Urbanized areas are larger than a single city or town but smaller than an MSA. The Tucson Urbanized Area covers much of the city of Tucson, all of South Tucson, and portions of the towns of Marana and Oro Valley. It also includes densely populated unincorporated areas directly around the city.
Urbanized areas are important because the main criteria for defining MSAs is the presence of an urbanized area with a population of 50,000 or more. An example of this is the Sierra Vista-Douglas MSA. It was designated as an MSA after the 2010 Census when the population of the Sierra Vista Urbanized Area had grown to over 50,000. While the city of Sierra Vista alone did not meet the population threshold (and still does not) the urbanized area extends beyond the city limits and exceeds a population of 50,000. This resulted in Cochise County moving from a micropolitan statistical area to an MSA. The same principle is true for urban clusters and micropolitan areas. The city of Safford does not quite meet the population threshold of 10,000, but the adjacent town of Thatcher combines into the urban cluster making it large enough for the micropolitan statistical area designation to be applied.
Wait – aren’t Cochise and Graham counties mostly rural? Yes! Any region that is not part of an urbanized area or urban cluster is considered rural. The majority of the land area in the Tucson MSA (Pima County) is also rural. Thus, metropolitan and micropolitan areas often include both urban and rural areas.
Another geographic layer are cities and towns. Pinal County has the largest number of incorporated cities and towns at 13, some of which overlap into surrounding counties. Apache Junction and Queen Creek, which are also located in Maricopa County, are an example of this. Cochise County has seven incorporated cities and towns, while Pima County has five, Yuma County has four, and Graham County has three. Greenlee and Santa Cruz tied with the least number of incorporated cities and towns at two each. Not everyone lives in cities and towns, however. Graham, Pinal, and Santa Cruz counties all have 50 percent or more of their population living outside of incorporated areas.
Pima County’s five incorporated cities or towns account for 65 percent of the county’s population. The other 35 percent of the population lives in unincorporated areas. Near Tucson, this includes well-established neighborhoods or places with a recognized concentration of population regarded much like a city or town even though they have never formally incorporated. The Census Bureau deems these as Census Designated Places (CDP), which is the statistical equivalent of an incorporated place. Because of this designation, we can obtain Census data for these areas. A good example of this in Southern Arizona is Green Valley – a community that has been around for a long time and is well established, but has no local government. Other examples included in MAP Dashboard community reports are Morenci in Greenlee County and Rio Rico in Santa Cruz County. Some are very small in population, such as Dateland in Yuma County or Elgin and Sonoita in Santa Cruz County. There are several CDPs in the Tucson area including: Corona de Tucson, Vail, Flowing Wells, Catalina, Catalina Foothills, Casas Adobes, Tanque Verde, and Picture Rocks. There are also CDPs in the western part of Pima County, which tends to be more rural and include unincorporated communities. Examples of these would be Sells, Ajo, Why, and San Miguel.
Sells and San Miguel are also within the Tohono O’odham Nation Reservation, which is another layer of geography in Southern Arizona. There are seven reservations that are within or overlap into Southern Arizona: Tohono O’odham, Pasqua Yaqui, Cocopah, Fort Yuma, Maricopa (Ak-Chin), Gila River, and San Carlos.
Other commonly used geographies include Census tracts and ZIP codes. See the Glossary below for more on these.
Figure 2 is an interactive map that displays the geographic regions located in Southern Arizona. The Tucson Urbanized Area is outlined in red, while all cities, towns, and CDPs are shown in blue. The name of the geographic region can be identified by scrolling over the map to produce a pop-up box. The map can zoom out to display the entire state of Arizona and will identify other geographic features, such as reservations.
Glossary of Census Geography Terms
American Indian Reservations – These areas have been set aside for the use of tribes and the boundaries defined by treaties, agreements, executive or secretarial orders, federal statutes, judicial determinations, or state governments. The Bureau of Indian Affairs maintains a list of all federally recognized tribal governments. The Census Bureau recognizes federal reservations (and associated off-reservation trust lands) as territory over which American Indian tribes have primary government authority. Reservations established by state governments must be defined within a single state, but federally recognized reservations can span several states, such as the Navajo Reservation.
Census Designated Place (CDP) – The Census refers to these as the “statistical counterpart of incorporated places”. These represent recognized concentrations of population that are not incorporated (i.e. do not have a municipal government). The Census Bureau, in cooperation with state and local officials, determines a boundary for the area and designates it as the equivalent of an incorporated city or town in order to compare to other places. An example of this in Southern Arizona would be Green Valley.
Census Tract – Census tracts are small statistical subdivisions of a county. Tracts generally cover an area with a population size between 1,200 and 8,000 people (average is 4,000), with the spatial size of the tract varying depending on the population density. They have boundaries designed to be consistent over a long time to make comparisons easier. There are instances where tracts split or merge because of population changes from one decennial census to the next but the numbering system typically allows for straightforward comparability.
City or Town – A type of incorporated place.
Incorporated Places – Established to provide governmental functions for a concentration of people – it is a governmental unit incorporated under state law having legally prescribed limits, powers, and functions. An incorporated place usually is a city, town, village, or borough, but can have other legal descriptions. They are always located within a single state or equivalent entity, but may extend across county boundaries.
Metropolitan Statistical Area – A Metropolitan Statistical Area (MSA) often referred to as a ‘metropolitan area’ consists of one or more counties with a primary city that has an urbanized area of at least 50,000 people along with any adjacent counties that have substantial social or economic integration, typically measured by commuting ties. Since counties in Arizona are very large, most of our MSAs consist of a single county. The only example in Arizona with multiple counties is the Phoenix-Mesa-Chandler MSA (often truncated to just Phoenix MSA for our purposes). It consists of both Maricopa and Pinal counties. In the case of the Phoenix MSA, several cities overlap the boundaries between Maricopa and Pinal counties and a large number of people commute between the counties for work. Many of the MAP Dashboard MSA’s contain multiple counties – for instance, the Denver MSA covers 10 counties!
Micropolitan Statistical Area – A micropolitan statistical area is similar to an MSA, only with a smaller population threshold. A micropolitan statistical area has at least one urban cluster with a population of at least 10,000 but less than 50,000. (Once an area hits the 50,000 mark, it becomes an MSA.) Both metropolitan and micropolitan areas are designated by the U.S. Office of Management and Budget (OMB).
Place – A term used to describe a concentration of population that is named, locally recognized, and not part of any other place, which would include both Census Designated Places (unincorporated) and cities or towns (incorporated).
Unincorporated Area – Portion of a county that is not included within the boundaries of a city or town. Census Designated Places can be included in and considered part of the unincorporated area of a county.
Urbanized Area – An urbanized area (UA) consists of densely developed territory that contains 50,000 or more people based on contiguous Census tracts with a specific population density threshold and accounts for commercial and other nonresidential urban land uses. The Census Bureau delineates UAs to provide a better separation of urban and rural territory, population, and housing in the vicinity of large places (i.e. what is not included in the urbanized area is considered rural). Urbanized areas are updated every ten years following the decennial census and form the core of a Metropolitan Statistical Area.
Urban Cluster – A smaller version of urbanized area with a population threshold of at least 2,500 people but less than 50,000.
ZIP Codes – ZIP Codes are a system set up by the U.S. Postal Service (USPS) to designate a particular postal delivery area. The Census Bureau uses ZIP Code Tabulation Areas (ZCTAs) as “approximate area representations” of the USPS ZIP Code service areas. In most cases, the ZCTA code is the same as the ZIP Code for an area. There are, however, instances where they are not the same. ZIP Codes that represent very few addresses or those assigned to businesses or a single delivery point are not included in ZCTAs. In general, it is much better to use Census Tracts to represent a small geographic area, as tract boundaries are designed by the Census Bureau to be maintained over a long period so that comparisons can be made over time and follow government boundaries (such as state or county) while ZIP Codes are strictly the purview of the USPS.