U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3040

April 2006

Geographic Analysis and Monitoring Program

National Urbanization Monitoring Assessment (NUMA)

A core geographic science element of the 

U.S. Geological Survey’s Geographic Analysis 

and Monitoring (GAM) Program is to monitor land-surface change for the Nation through 

time.

The Nation’s land surface is dynamically evolving and transitioning in response 

to natural and human processes. The need 

to understand the transformations and locations where changes are taking place, their 

underlying causes, and the rate at which the 

transitions are occurring is fundamental to the 

health and viability of the Nation’s natural and 

developed environments.

Development of a systematic urbanization monitoring capability is a fundamental 

requirement to increasing our understanding of 

human-induced land transformations that are 

occurring on the Nation’s landscape and the 

possible consequences that may result in the 

future from continued urban land-use transitions.

Land-use policy decisions in both urban 

and rural landscapes influence and shape how 

these natural and human environments respond 

to landscape change processes. Thus, the 

GAM Program needs to have the capability to 

monitor, analyze, estimate, and forecast temporal states of the Nation’s urban form in order to 

provide the scientific foundation for managing 

the Nation’s land and natural resources.

Environmental and Societal Issues

The U.S. population has become more urban 

each decade through the 20th century. Most of the 

urbanization through time has occurred in suburban and exurban landscapes (that is, non-metropolitan counties) and is less a result of land-use 

development in metropolitan counties. As rural 

populations migrated to predominantly urbanized 

landscapes, metropolitan areas became the catalyst 

for urbanization driven by population and economic 

growth. The improvement in telecommunications 

and attraction to natural and cultural amenities has 

resulted in urban development spreading into regions 

where few inhabitants resided prior to 1990.

According to research by the Metropolitan 

Institute at Virginia Tech University, between 1960 

and 2000 the Nation’s urbanized population grew 

by about 80 percent, and the urbanized land area 

grew by about 130 percent. From 1985 to 2001, 

U.S. Housing and Urban Development and Census 

Bureau data quantify that about 40 percent of the 

19 million new housing units built were on lots of 

0

20

40

Urban population, in percent 60

80

100

1900 1920 1940 1960

Census year

1980 2000

United States

Texas

Analysis of 20th century urban population composition 

for the United States and State of Texas.

Land-use development near Berthoud, Colorado.
1 acre or larger. Each year the Nation converts more 

than 3,000 square miles of land to large-lot residential development. The suburbs of the 1970s now act 

as “anchors,” according to research by the Brookings 

Institution Metropolitan Policy Program, and project 

population growth even farther away from urban 

cores. The more affordable land on the periphery of 

the urbanized area is encouraging low-density landuse development on the farthest edges of metropolitan areas.

Research Assumptions

Metropolitan areas continue to be the economic 

engines driving regional urbanization, and urban 

growth follows economic growth.

Transformation of the natural land surface and 

subsequent urbanization tend to follow population 

and housing densification thresholds. Extension and 

improvement in the existing urban infrastructure 

enable this land transformation. Regions experiencing economic growth evolve from rural and 

exurban densities to suburban and urban land-use 

patterns.

 Low-density land-use development on the urban 

fringe and in unincorporated rural areas is occurring 

at a faster rate than urbanization in the denser urban 

and suburban environments.

Local land-use policies and land-use zoning 

densities for unincorporated areas encourage lowdensity growth on the urban fringe, and these areas 

will eventually become “exclusion zones” to denser 

urbanized landforms.

Low-density land-use development on the urban 

fringe has an increased per capita demand for natural 

resources and urban services. This disproportionate 

increase in lower density development results in 

greater effects on landscape fragmentation, ecological 

and socioeconomic processes, and tax revenues.

Regions with the highest demographic and 

socioeconomic growth rates should be the areas in 

the Nation experiencing the most rapid urbanization. This research assumption should be verifiable 

by investigating parameters such as gross regional 

product and population.

Research Hypotheses

Do urbanization growth rates, urban-form 

patterns, land-use trends, and migration patterns 

vary between U.S. Department of Commerce 

1.

Housing unit density transitions, 1990­–2000, Austin–

Round Rock metropolitan statistical area, Texas.

No transition

EXPLANATION

Transitioned to urban

Transitioned to suburban

Transitioned to exurban

Transitioned to rural

0 10 20 30 MILES

U.S. population and gross regional product (GRP) 

average growth rates computed for economic areas.

Boundary of BEA

 economic areas

Greater than 1.5 standard

 deviations

0.5 to 1.5 standard

 deviations

-0.5 to 0.5 standard

 deviations

-1.5 to -0.5 standard

 deviations

Less than -1.5 standard

 deviations

EXPLANATION

0 300 600 MILES

Average population and GRP change 1977−2003

Standard deviations
Bureau of Economic Analysis (BEA) Economic 

Areas (EA) and Economic Regions?

Does the primary Core-Based Statistical Area 

(CBSA), acting as the economic engine, cause 

urbanization patterns, rates, and trends to vary 

between EAs?

Can temporal land-use transition probabilities 

be used to forecast when county-based Department of Agriculture Economic Research Service 

Rural-to-Urban Continuum Codes (RUCC) will 

change urban-form classification within each 

EA?

Are specific EAs and RUCC subregions within 

each EA placing greater urbanization demands 

on the environment and creating more societal 

pressures for those urbanizing regions?

2.

3.

4.

Relevance and Effects

Land-use development affects how planners and 

resource managers address issues exacerbated by 

increased urbanization. Environmental and societal issues are being accelerated by human-induced 

land transformations. These issues include loss 

of ground-water recharge zones, increased traffic 

congestion, loss of arable land, increased air pollution and ozone levels, depletion of endangered 

and threatened species native habitat, and increased 

exposure of humans to catastrophic natural and manmade hazards.

Strategy and Approach

The research methodology entails classifying 

EAs using CBSA population threshold tiers and 

stratifying EAs with computed average population 

and gross regional product (GRP) growth rates from 

1977 to 2003. This technique provides a systematic 

nationwide structure for sampling and monitoring 

urbanization within EAs.

The short-term research approach was to select 

two economic areas experiencing rapid urbanization 

as prototype case studies. This selection was based 

on computed and ranked average population and 

GRP growth rates.

U.S. economic regions and areas.

Far West

Great Lakes

Lower Mississippi

EXPLANATION

0 300 600 MILES

Mid-Atlantic

New England

Plains

Bureau of Economic Analysis

Revised BEA Economic Regions

Rocky Mountain

South Atlantic

Southwest

Canyon Ridge Springs planned urban development 

west of Austin, Texas.

Austin–Round Rock and San Antonio economic areas.

0 100 200 MILES

Bureau of Census urban areas

EXPLANATION

BEA EA 144 counties

BEA EA 13 counties

US counties

National Urbanization

Monitoring Assessment

(NUMA)

Bureau of Economic Analysis (BEA)

Economic Areas (EA) 13 and 144

in Texas

0 100 200 MILES

Bureau of Census urban areas

EXPLANATION

BEA EA 144 counties

BEA EA 13 counties

Texas counties

National Urbanization

Monitoring Assessment

(NUMA)

Bureau of Economic Analysis (BEA)

Economic Areas (EA) 13 and 144

in Texas
Prototype study sites selected were the Austin–

Round Rock, Texas, and the San Antonio economic 

areas. These EAs were respectively ranked 3d and 

34th nationally. Both of these economic areas in 

Texas are classified as major metropolitan CBSAs 

with a total population greater than 1 million residents by the University of Arizona.

The Austin and San Antonio EAs were subdivided into urban, suburban, exurban, and rural 

landscapes using the RUCC codes. To quantify 

urbanization rates, patterns, trends, and human 

migration paths, indicators were extracted from a 

USGS database as a potential standard template for 

monitoring human-induced land transformations.

Human migratory paths computed from decennial population information, and temporal land-use 

and land-cover (LULC) data were used in conjunction with land-use trends analysis (LUTA) metrics to 

understand the factors and causes influencing urbanization within an EA. Comparative analysis between 

RUCC subregions and EAs was conducted as a final 

step in the urbanization monitoring assessment.

Geographic Research Results

In order to characterize 1977 to 2000 urbanization for the Austin and San Antonio EAs, existing 

USGS Geographic Information Retrieval and Analysis System (GIRAS), National Land Cover Data 

(NLCD), and U.S. Census Bureau datasets provided 

the temporal foundation for LUTA metrics.

Analysis of the Exurban RUCC subregion 

for the San Antonio EA indicates that approximately 34 percent of the landscape transitioned to 

another LULC category from 1977 to 2000. The 

most frequent LULC category becoming urbanized 

was grassland/shrubland. Within this timeframe, 

urbanization in the Exurban subregion of the San 

Antonio economic area occurred at an annual rate of 

about 1.8 percent. In comparison, forest/woodland 

decreased at a rate of approximately 2.1 percent per 

year. 

Human migration trends for population and urban 

area (UA) centers of mass were calculated respectively by using county-level population data from 

the U.S. Census Bureau and temporal USGS LULC 

datasets. The Austin–Round Rock and San Antonio 

Metropolitan Statistical Areas (MSAs) were used as 

migration case study sites.

Research results for the Austin–Round Rock 

MSA illustrate that population growth in Williamson 

County is the primary driver 

of northerly migration trends 

for the urban RUCC subarea within the Austin EA. 

In comparison, the direction 

of the Austin–Round Rock 

MSA temporal urbanized-area 

migration path demonstrates 

a northwesterly direction due 

to the influence of land-use 

development around U.S. 

Highways 281 and 183 

transportation corridors.

For More Information

Contact Dave Hester, USGS–Rocky Mountain 

Geographic Science Center, 303–202–4318,

dhester@usgs.gov

Land-use transitions (1977 to 2000) for the exurban portion of the San Antonio Economic 

Area.

LULC Transitions (in acres)

1977 to 2000

2000 LULC Class

1977 LULC Class Water

Urban/

Developed

Barren

Land

Forest/

Woodland

Grassland/

Shrubland Agriculture Wetlands Unclassified Total acres

Water 25,378 225 50 450 6,886 506 21 0 33,515

Urban/Developed 0 53,051 0 0 0 0 0 0 53,051

Barren Land 75 1,722 1,082 1,612 6,876 617 14 0 11,999

Forest/Woodland 2,461 3,838 7,151 745,892 713,581 32,232 758 0 1,505,912

Grassland/Shrubland 17,128 14,490 25,765 156,337 3,740,262 125,462 1,895 0 4,081,339

Agriculture 1,660 7,365 3,900 16,755 213,903 261,423 470 0 505,475

Wetlands 154 6 13 101 1,797 125 1,581 0 3,778

Unclassified 1,205 39 5 205 129 95 4 0 1,682

Total acres 48,060 80,736 37,964 921,353 4,683,434 420,459 4,743 0 6,196,751

Comparative analysis between Austin–Round Rock MSA 

population and urbanized area migration paths.