For Ohio, we have operationalized two of measures to identify the Ohio exurban landscape: commuting distance and population density.
Exurban Ohio defined by commuting distance from urban centers - (description below)
Exurban Ohio defined by population density - (description below)
Determining Exurbia by Commuting Distance:
To define the exurban field in Ohio, three noteworthy decisions were made. First, since we are interested in comparisons among politically defined geographic entities, townships, villages and cities are our units of analysis. Second, we opted to define the exurban field via a simple distance model structured according to what we determined as reasonable commuting distances to the nearby urbanized area. Finally, we decided that the exurban field was associated with large urbanized areas, specifically urban areas with populations greater than 50,000 residents. All of these decisions have drawbacks, but our overall approach is consistent with previous research (Audirac, 1999).
The exurban “field” extends from the boundary of each of the state’s urbanized areas and those urbanized areas in neighboring states and extends outward to what might be considered a reasonable commuting distance back to the urbanized area. The commuting distance was determined by analyzing commuting data from the 2000 U.S. Census. First, the average commute time was calculated for all areas of Ohio. Given the size range of urbanized areas in the state, it was expected that commuting times would vary according to the population of the urbanized area. Commuting times were examined for all urbanized areas and average commutes were found to be longer around the largest urbanized areas and shorter around the smallest urbanized areas. To account for this variation, the commuting field was defined as 35 miles from the edge of the largest urbanized areas (one million or more residents); 25 miles from the edge of urbanized areas with a population between 500,000 and one million people; and 15 miles from the edge of urbanized areas of less than 500,000 residents.
To distinguish the inner and outer zones of the exurban field, a break was created at half the distance from the urban edge and the outer portion of the exurban field (this break was at 17.5 miles for urbanized areas of over one million; 12.5 miles for urbanized areas of between 500,000 and one million people; and 7.5 miles for all other urbanized areas). Once the inner exurban and outer exurban fields were determined, the 931 cities or villages (incorporated places) and 1,309 townships (unincorporated places) were assigned to the urban, suburban, inner exurban, outer exurban, or rural field. The 17 central cities of urbanized areas located in the state were assigned to the urban field. Cities other than core cities, villages and townships with at least 25% of their land area within the urbanized area were defined as part of the suburban field. Inner exurban cities, villages, and townships were those places not defined as suburban with at least 25% of their land base in the inner exurban field. Outer exurban cities, villages and townships were those places not assigned to the inner exurban field and with at least 50% of their land base within the outer exurban field. Finally, rural cities, villages and townships were those places without at least 50% of their land base in the exurban field.
The result is that 17 core cities were defined as urban, 268 cities and villages and 82 townships were classified as suburban, 235 cities and villages and 482 townships were classified as inner exurban, 206 cities and villages and 340 townships were classified as outer exurban, and 205 cities and villages and 404 townships were classified as rural. Figure 1 reveals the spatial organization of Ohio’s cities, villages, and townships into the fields of interest and Table 1 reports basic population data for the nine groupings of interest derived by this classification scheme. The majority of Ohio’s population is concentrated in the core or suburban cities, villages and townships (more than seven million residents). The core cities have experienced population decline between 1980 and 2000, while the suburban cities and villages and suburban townships have grown. Relative and aggregate population growth has been greatest in the suburban townships of the state from 1980 to 2000. Inner exurban townships are home to nearly 1.5 million residents, up from 1.3 million in 1980. Population growth in the inner exurban cities and villages has been much more modest since 1980. Outer exurban cities and villages collectively lost population between 1980 and 2000, while outer exurban townships have collectively grown nearly 14%. Rural cities, villages, and townships account for less than a million of the state’s residents in 2000.
Determining the Density of Urban, Suburban, Exurban and Rural Settlement:
To perform the analysis, population density for each block group in Ohio was calculated for the years 1970, 1980, 1990, and 2000. Each block group was designated as an urban, suburban, exurban or rural area for each decade based on population density thresholds.
High-density urban areas were defined as all block groups with population densities of 5,000 or more persons per square mile; this is equivalent to less than 1/3 acre per housing unit. Low-density urban was defined as all block groups with a density of 1,000 to 5,000 persons per square mile or 1/3 to 1.5 acres per housing unit. The U.S. Census Bureau’s definition of urban land was used to guide the definition of these population density thresholds. Urban land, as defined by the U.S. Census Bureau, includes all block groups or blocks with a population density of at least 1,000 people per square mile that are surrounded by census blocks with at least 500 people per square mile. For the purpose of this analysis, the Census standard of 1,000 people per square mile serves as the dividing line between urban and suburban areas. To differentiate between the core urban areas and higher density early suburban neighborhoods, areas with a population density of 5,000 persons per square mile or more were classified as Urban High Density.
Suburban areas were determined to be block groups with a density of 325 to 1,000 persons per square mile (1.5 to 5 acres per housing unit) and exurban areas were defined as all block groups with a density of 40 to 325 persons per square mile (5 to 40 acres per housing unit). The dividing line between suburban and exurban (5 acres per housing unit) was determined based on state law, which emphasizes the unique nature of the 5-acre lot size in land use regulation. Under traditional Ohio law, lots greater than 5 acres are exempted from local subdivision regulations.
Finally, rural areas were all block groups with a population density of less than 40 persons per square mile or 40 or more acres per housing unit. The 40-acre minimum per housing unit that was used to define rural areas was based on an approximation of the minimum amount of acreage necessary to successfully support agriculture. A 40-acre lot size was deemed conservative because it is well below the average acreage of a farm in Ohio in 1999 (186 acres) and it is also smaller than the average farm size in Ohio’s traditionally urban counties (average farm size in Hamilton, Montgomery and Summit counties in 2000 was 88 acres, 125 acres and 63 acres respectively).16 Also, a national survey of large minimum lot size zoning provided by the “Farmland Information Library’s State Farmland Protection Database” defines large lot zoning for agriculture as “typically at least 20 acres in the eastern United States and at least 35 acres in other regions”.