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Human migration analysis of the Austin-round rock and San Antonio, Texas, economic areas.

Abstract: The Austin-Round Rock and San Antonio Economic Areas have experienced major population growth and land-use development in recent decades. With this ongoing increase in human presence and activity comes a variety of impacts on the natural and built environments. This research examines how commonly available data describing socioeconomic, demographic, and land-use development conditions from the regional to local levels can be used to measure and visualize various phenomena of human migration and, in turn, be used to focus the efforts of planners, land managers, decisionmakers, and researchers on geographic areas both currently experiencing and anticipated to experience the continuing and increasing effects of the human presence on the landscape. The methods described provide both a flexible framework for analyzing aspects of human migration at various geographic and temporal scales and a portable framework that can be applied to regions across the Nation.

RESEARCH ISSUE

This research examines how commonly available national, regional, and local data describing socioeconomic, demographic, and land-use development can be leveraged for the analysis of human migration trends. Using a series of quantitative metrics and visualization techniques, human migration trends within the Austin-Round Rock Economic Area (EA) are described and measured over various geographic and temporal scales, and a preliminary comparison to population migration trends within the San Antonio EA is completed. The effectiveness of such an analysis for assisting in the investigation of the social, economic and political influences of and responses to temporal changes in the direction, distance, and migration rates of population and urban-area centers of mass is also considered.

The concept of using the center of mass as a quantitative metric for investigating historical population distribution and change was developed by the U.S. Census Bureau. A population center of mass represents a balance point at which an imaginary, weightless, rigid, and flat land surface would balance if each individual person placed on it had an equal weight (U.S. Census Bureau, 2001). This concept can be extended to the investigation of urban-area centers as well. An urban-area center of mass represents a geographic center where the urban or developed land surface would balance assuming it were a plane with each urban land unit (i.e., urban pixel) having an equal weight.

The analysis of these population and urban-area center migrations is augmented by the incorporation of data representing the magnitude and direction of population flows within and outside the subject EAs. These flows can illustrate human migrations occurring over a multiyear basis or a typical workday. This research attempts to demonstrate how these data, analyzed across a series of specifically defined geographic extents, might be used by regional and local planners, land managers, and decisionmakers and by other researchers. Employment of such methods could assist in describing the dynamics of human movement and land-use development within a region of interest, identifying localized areas where human activities are driving landscape change over the broader region, prioritizing areas according to effects on the natural and built environments (e.g., water-supply sources, hazard exposure, infrastructure needs, etc.) resulting from human activities and developing models that enhance capabilities to forecast the sources of these drivers and location of various consequences into the future.

METHODOLOGY

Study Area and Subarea Definitions

The Austin-Round Rock and San Antonio EAs (Figure 1) are two of 179 county-based regions defined by the Bureau of Economic Analysis (BEA) according to the presence of one or more economic nodes (i.e., a metropolitan or micropolitan statistical area), commuting patterns, and, in some cases, newspaper circulation data (Bureau of Economic Analysis, 2004a). EAs were selected as the regional construct for this analysis because they provide a complete national coverage and have been relatively stable over time as compared to other functional region definitions such as Metropolitan Statistical Areas (MSA). This national coverage facilitates the application of methodologies developed in this research to regions across the United States. The county-based structure of the EAs, while simplifying the compilation of socioeconomic and demographic data, allows for the aggregation of multicounty subregions within EAs or the disaggregation of the analysis to subcounty units such as census tracts or block groups as needed for subsequent research.

The selection of the EAs included in this analysis was based on their relative sizes and their growth in recent decades. The primary cities, Austin and San Antonio, have increased from the 54th to 16th largest and the 15th to 9th largest cities in the Nation, respectively, between 1970 and 2000. As of Census 2000, the 11 component counties of the Austin-Round Rock EA had a total population exceeding 1.3 million, and the 23 counties of the San Antonio EA were home to slightly fewer than 2 million people (U.S. Census Bureau, 2000a).

[FIGURE 1 OMITTED]

For portions of the analysis, the Austin-Round Rock EA counties were grouped into subareas on the basis of Rural-Urban Continuum Codes (RUCC) previously developed by the Economic Research Service (ERS) (Economic Research Service, 2003). The RUCC codes apply to counties and represent nine categories of population levels and adjacency to metropolitan areas. These nine RUCC codes were used to categorize counties as urban, suburban, exurban, or rural (Carruthers and Vias, 2005). The purpose of this categorization was to identify and distinguish the counties within the EA that are seemingly more urban in terms of population and location relative to the urban core. This allowed for comparison of migration trends in these urban counties with those of the entire EA. It should also be noted that these urban counties correspond to those counties comprising the Austin-Round Rock MSA. This holds true for all EAs, that the counties identified as urban from RUCC codes are also the EA's MSA counties. In this manner, the categorization of the RUCC codes can serve as a convenient bridge between existing or new analyses completed at the MSA and EA levels. The categorization also serves to illustrate a possible means of stratifying counties within an EA for future research relating to how human migration, land-use development, and other factors might be characterized at different points along an urban-to-rural gradient.

The counties classified as urban (Figure 2) were further categorized by census tract according to Rural-Urban Commuting Area Codes (RUCA) (Economic Research Service, 2000). The RUCA codes distinguish census tracts by both population levels and commuting flows. They are used here to illustrate just one example of the application of human migration analysis at the subcounty level.

Finally, a 1:24,000 scale, 16-quadrangle area encompassing the Austin-Round Rock EA's urban core (Figure 3) was included in the analysis in order to measure and visualize the migration of the urban-area centers within a more localized and intensively developed area of the EA (i.e., the City of Austin). Here it must be noted that while the land-use/land-cover (LULC) data used for this portion of the analysis were derived from commonly available data sources, these data underwent additional processing before use in the current analysis. Additionally, while the geographic extent of this 16-quadrangle area does not follow the county-based pattern previously established, it serves to illustrate how other geographic frameworks can be integrated into the analysis by using comparable quantitative metrics and visualization techniques and providing yet another opportunity for comparative analysis.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Data Sources

To calculate population centers of mass, county-level population data from 1970 to 2000 were obtained from the U.S. Census Bureau's American FactFinder and Population Estimates Archives websites (U.S. Census Bureau, 2004). County-level decennial population projections from 2010 to 2040 were also obtained (Texas State Data Center and Office of the State Demographer, 2004).

The data used to calculate urban area centers of mass were derived from thematically classified, remotely sensed LULC data. Geographic Information Retrieval and Analysis System (GIRAS) data, derived from aerial photos, served as the 1977 LULC vintage (U.S. Geological Survey, 1977). National Land Cover Dataset (NLCD) data, derived from satellite imagery, provided 1992 vintage LULC data (U.S. Geological Survey, 1992). The disparate formats, resolutions, and classification schemes of these two datasets required their standardization to a single format, resolution, and classification scheme. Twenty-three Anderson Level II categories of GIRAS data and 21 Anderson Level II categories of NLCD data were aggregated into 8 Anderson Level I categories with those pixels classified as urban/developed serving as the basis for urban-area center of mass calculations. Both datasets were resampled to a 30-meter resolution.

Census urban-area boundary files were used as the 2000 vintage data (U.S. Census Bureau, 2000b). While these urban area boundaries are based on population densities rather than remotely sensed data, they were used as a proxy to approximate urban/developed land. The source dataset was converted from a vector format to a 30-meter resolution raster dataset for comparison to the GIRAS and NLCD data. By its nature, the Census urban-area data included only the urban/developed category, which was sufficient for urban-area center of mass calculations. In the case of the 16-quadrangle area, previously classified Landsat 5 Multi-Spectral Scanner (MSS) and Landsat 7 Thematic Mapper (TM) satellite imagery were used to calculate an additional set of urban-area centers of mass for the years 1983, 1991, 1997, and 2000 (Trelogan, Kintz and Harris, 2003).

Additional data regarding intercounty migration between 1995 and 2000 were obtained from Census special tabulations (U.S. Census Bureau, 2000c). Intercounty commuting data spanning 1970 to 2000 were based on Census journey-to-work data as compiled by the BEA (Bureau of Economic Analysis, 2004b). Finally, RUCC and RUCA code data were obtained as described previously.

Population Center of Mass

Population centers of mass were calculated by joining the historical and projected county population data to county boundary polygon shapefiles of the Austin-Round Rock and San Antonio EAs. The mean population centers were calculated separately for each EA as the average coordinates of all county centroids within each EA weighted by the county population values for each decennial Census count or decadal projection. This process was repeated for the Austin-Round Rock EA's urban counties as identified by RUCC codes and corresponding to the Austin-Round Rock MSA.

A text file containing the population center of mass coordinates was then used to generate a set of line shapefiles with each line segment representing the migration path between subsequent population centers. The length and bearing of these paths were calculated using coordinate geometry in order to generate distance, direction, and migration-rate metrics for each geographic area.

While this approach does not take into account the exact location of populations within each county, at the regional scale, the general direction of the migration trends relative to each county can be measured and visualized. The general methodology remains the same when applied to subcounty units such as census tracts or block groups. This would, of course, allow for a refinement of the migration metrics and enhance the comparability between population and urban-area centers over more localized areas.

Urban-Area Center of Mass

Urban-area centers of mass were calculated for the full Austin-Round Rock EA, its urban counties (i.e., the Austin-Round Rock MSA), and the 16-quadrangle area of its urban core by extracting urban pixels from the LULC data, converting these pixels to a series of point shapefiles, and calculating the mean center of these points. The method previously described to generate the population-center migration paths and metrics was also used to generate these paths and metrics for the urban-area centers. The coordinates of the projected urban-area centers of mass associated with the 16-quadrangle area were obtained from previously executed SLEUTH model output. SLEUTH includes both Urban Growth Model (UGM) and land-cover deltatron model (LCD) components that operate on slope, land cover, exclusion, urbanization, transportation, and hillshade input layers to simulate future urban growth and land-cover change within a region (U.S. Geological Survey, date unknown). The urban-area center coordinates are included in the model's statistical data output files.

Migration and Commuting Flows

Visualization of migration flows into, out of, and within the Austin-Round Rock MSA between 1995 and 2000 was accomplished by subtracting county outflow data from county inflow data to generate net migration flow values for each county. These values were joined to a set of line-segment shapefiles representing flow paths both internal and external to the Austin-Round Rock MSA. The line segments were then symbolized to represent the net direction and relative magnitude of migration flows for each county. The analysis of these migration flows was limited to the 1995-2000 period as the source flow files are based on special tabulations compiled by the U.S. Census Bureau that were not readily available without additional cost for earlier vintages at the time the analysis was completed.

The same methods were used to visualize the commuting flows for the Austin-Round Rock MSA. In this case, the calculated values are representative of daily net commuting flows as measured by the Census from 1970 to 2000. As a result, the changes in these commuting flow patterns are observable over time.

RESULTS

Regional Analysis: Austin-Round Rock Economic Area

The historical and projected migration metrics of the Austin-Round Rock EA are given in Table 1. As illustrated in Figure 4, the extent of the Austin-Round Rock EA's population-center migration is contained within Travis County where the City of Austin is located. There has been a northerly trend in population-center migration along the Interstate 35 corridor and towards Williamson County since 1970. This trend reflects the rapid population growth that has occurred in Williamson County in recent decades. Population projections suggest this regional migration path will continue on a similar trajectory at least through 2040.

[FIGURE 4 OMITTED]

Population Growth and Migration

The line graph (Figure 5) shows historical and projected population from 1970 to 2040 for each of the EA's component urban counties or MSA. The data indicate that, while Travis County is anticipated to remain the most populous in the MSA, Williamson County is anticipated to experience the highest rate of growth, over 200%, based on a population increase of more than 500,000 between 2000 and 2040.

The flow map (Figure 6) illustrates the large contribution of inflow migration from outside the Austin-Round Rock MSA (Table 2) to Williamson County population growth from 1995 to 2000. Net inflows to the county are represented by the green arrows and net outflows are represented by the red arrows. Due to rounding, inflow and outflow percentages might not total to exactly 100.0%. Williamson County's net migration was an inflow of 47,669. To estimate net migration flows from a source or to a destination, multiply the flow percentage by the net migration value (e.g., 29.6% x 47,669 = 14,110 flow from Travis County to Williamson County).

[FIGURE 6 OMITTED]

Austin-Round Rock Migration Extent

Tables 3-5 and Figure 7 summarize population and urban-area center migration metrics for the Austin-Round Rock EA (yellow), MSA (blue), and the City of Austin's urban-area core (red). The predominantly northern component of each of these migration paths can be attributed to the rapid population growth and associated development in Williamson County. The western component of the urban-area center migrations can be explained, in part, by development around Lake Travis west of Austin and along transportation corridors such as U.S.

Highways 183 and 290. The similarities between the EA's and the City of Austin's urban-area migration trends as well as those between the MSA's and the EA's population-migration trends as previously illustrated in Figure 4 indicate the influence of the urban-area core and the MSA counties over regional trends.

[FIGURE 7 OMITTED]

Commuting: The Daily Migration

U.S. Census Bureau worker flow files provide a snapshot of what is generally the daily movement of individuals from their county of residence to their county of work. These flow patterns can help define functional ties between counties and within regions as well as indicate areas where transportation infrastructure and the surrounding environment may be subjected to increasing stress. The 1970 to 2000 time series (Figure 8) demonstrates how Williamson County has evolved from a net outflow to a net inflow county for workers from outside the Austin-Round Rock MSA (Table 6). Simultaneously, commuting ties to Travis County have continued to strengthen. Net inflows to the county are represented by the green arrows and net outflows are represented by the red arrows. Due to rounding, inflow and outflow percentages might not total to exactly 100.0%. Williamson County's net commuting was a net outflow of 3,222 in 1970, 15,493 in 1980, 35,037 in 1990, and 37,969 in 2000. To estimate net commuting flows from a source or to a destination, multiply the flow percentage by the given net outflow value (e.g., -110.9% x 37,969 = -42,108 flow from Williamson County to Travis County in 2000).

[FIGURE 8 OMITTED]

RUCA codes are a census tract-level classification scheme used by the ERS to identify urban cores and economically integrated adjacent areas by using criteria including population density, urbanization, and daily commuting. A review of the MSA's RUCA codes (Figure 9) reveals the increased integration of outlying areas with the metropolitan core between 1990 and 2000. This is particularly evident in Williamson County where the rural area surrounding Granger and the large town core of Georgetown have seen their primary commuting flows shift to Austin's urban-area core. Texas Highway 130 (in red), a toll road and future portion of the Trans-Texas Corridor-35 (TTC-35) under construction east of Austin, might prove to integrate additional area into the Austin metropolitan core as defined by these RUCA codes.

[FIGURE 9 OMITTED]

Comparative Analysis: San Antonio Economic Area

A comparison of Austin-Round Rock and San Antonio EA population center migration (Table 7, Figure 10) reveals a slower projected migration in the latter. Unlike the influence that Williamson County has on the Austin-Round Rock EA population-center migration path, the San Antonio EA population center remains nearly static through 2040 as a result of the magnitude of projected population growth within Bexar County relative to the remainder of the EA.

[FIGURE 10 OMITTED]

CONCLUSION

Results of the analysis demonstrate how human migration trends can be used to focus land use and socioeconomic research questions to increasingly finer geographic (region, county, census tract, etc.) and temporal (decadal, annual, daily, etc.) scales. Regional analysis of the Austin-Round Rock EA reflected Travis County's status as the location of the region's largest city and the State's capital, Austin. The Austin-Round Rock EA's population and urban-area centers of mass are both located here. However, a more detailed analysis revealed population growth and urban development in Williamson County as a primary driver of migration trends in recent decades and likely for decades to come. With such findings, future research questions might be formulated to target localized areas and specific scenarios such as:

Can projected commuting flow patterns disaggregated by industry be used to model the consequences of socioeconomic drivers on land use along specific transportation corridors?

What patterns of land-use development might be induced or enabled by the completion of Texas Highway 130 / TTC-35?

What policy responses might prove most effective for shaping future economic and land-use development both regionally and locally?

REFERENCES

Bureau of Economic Analysis. 2004a. 2004 Redefinition of the BEA Economic Areas. U.S. Department of Commerce. Washington, DC. <http://www.bea.gov/bea/ARTICLES/2004/11November/1104Econ-Areas.pdf> Accessed July 13, 2006.

Bureau of Economic Analysis. 2004b. Regional Economic Accounts. Census Journey to Work. U.S. Department of Commerce. Washington, DC. <http://www.bea.gov/bea/regional/reis/jtw/default.cfm> Accessed June 22, 2005.

Carruthers, John I. and Alexander C. Vias. 2005. Urban, Suburban, and Exurban Sprawl in the Rocky Mountain West: Evidence from Regional Adjustment Models. Journal of Regional Science. Vol. 45. No. 1. pp. 21-48.

Economic Research Service. 2000. Rural-Urban Commuting Area Codes. U.S. Department of Agriculture. Washington, DC. <http://www.ers.usda.gov/Data/RuralUrbanCommutingAreaCodes/> Accessed July 24, 2006.

Economic Research Service. 2003. Measuring Rurality: Rural-Urban Continuum Codes. U.S. Department of Agriculture. Washington, DC. <http://www.ers.usda.gov/Briefing/Rurality/RuralUrbCon/> Accessed July 24, 2006.

Texas State Data Center and Office of the State Demographer. 2004. Texas Population Projections Program. Institute for Demographic and Socioeconomic Research (IDSER). College of Public Policy. The University of Texas at San Antonio. < http://txsdc.utsa.edu/tpepp/2004projections/> Accessed June 12, 2006.

Trelogan, J., D.B. Kintz, and S. Harris. 2003. Visualizing the Austin Region: Urban Growth, 1983-2000. Poster. University of Texas School of Architecture, Community and Regional Planning Department. University of Texas at Austin.

U.S. Census Bureau. 2000a. American FactFinder, Summary File 1. U.S. Department of Commerce. Washington, DC. <http://www.factfinder.census.gov> Accessed June 8, 2006.

U.S. Census Bureau. 2000b. Cartographic Boundary Files. U.S. Department of Commerce. Washington, DC. <http://www.census.gov/geo/www/cob/bdy_files.html> Accessed June 15, 2006.

U.S. Census Bureau. 2000c. County-to-County Migration Flow Files. U.S. Department of Commerce. Washington, DC. <http://www.census.gov/population/www/cen2000/ctytoctyflow.html> Accessed July 25, 2006.

U.S. Census Bureau. 2001. Centers of Population Computation for 1950, 1960, 1970, 1980, 1990 and 2000. U.S. Department of Commerce. Washington, DC. <http://www.census.gov/geo/www/cenpop/calculate2k.pdf> Accessed August 14, 2006.

U.S. Census Bureau. 2004. Population Estimates Archive. U.S. Department of Commerce. Washington, DC. < http://www.census.gov/popest/archives/> Retrieved June 8, 2006.

U.S. Geological Survey. 1977. Land Use and Land Cover (LULC). FTP download. Earth Resources Observation and Science (EROS) Data Center. Sioux Falls, SD. <http://edc.usgs.gov/products/landcover/lulc.html> Accessed June 15, 2006.

U.S. Geological Survey. 1992. National Land Cover Dataset (NLCD). Multi-Resolution Land Characteristics Consortium Project. Earth Resources Observation and Science (EROS) Data Center. Sioux Falls, SD. < http://www.mrlc.gov/index.asp> Accessed June 15, 2006.

U.S. Geological Survey. Date unknown. Project Gigalopolis: Urban and Land Cover Modeling Website. <http://www.ncgia.ucsb.edu/projects/gig/project_gig.htm> Accessed June 8, 2006.

Ben C. Sherrouse

Rocky Mountain Geographic Science Center

U.S. Geological Survey

Denver, CO 80225

303-202-4072

303-202-4354

bcsherrouse@usgs.gov

David J. Hester

Rocky Mountain Geographic Science Center

U.S. Geological Survey

Denver, CO 80225

303-202-4318

303-202-4354

dhester@usgs.gov
TABLE 1: AUSTIN-ROUND ROCK EA POPULATION CENTER OF MASS
MIGRATION METRICS [D, DEGREE; M, MINUTE; S, SECOND; YR, YEAR;
N, NORTH; W, WEST; E, EAST]

 Migration Distance
 Mean Center Mean Center from Previous
Years North Latitude West Longitude Population Center
Mapped (D-M-S) (D-M-S) (meters)

1970 30-17-31 -97-44-4
1980 30-18-21 -97-44-14 1,564
1990 30-18-42 -97-44-13 652
2000 30-19-26 -97-44-16 1,356

 Projected

2010 30-19-35 -97-44-7 390
2020 30-19-52 -97-43-53 637
2030 30-20-14 -97-43-38 796
2040 30-20-37 -97-43-22 815

 Migration Direction Annual
 from Previous Population Center
Years Population Center Migration Rate
Mapped (bearing: D-M-S) (meters/yr)

1970
1980 N 8-43-16 W 156
1990 N 4-24-54 E 65
2000 N 3-13-29 W 136

 Projected

2010 N 41-5-1 E 39
2020 N 36-16-31 E 64
2030 N 32-7-53 E 80
2040 N 31-32-13 E 81

Some mapped centers might be obscured where migration distances are
relatively short.

TABLE 2: EXTERNAL MIGRATION TO
THE AUSTIN-ROUND ROCK MSA

Source 1995-2000

San Antonio MSA 1,846
Other Texas Counties 12,739
United States 18,954

TABLE 3: AUSTIN-ROUND ROCK EA URBAN-AREA CENTER
MIGRATION METRICS (YELLOW PATH IN FIG. 7) [D, DEGREE; M,
MINUTE; S, SECOND; YR, YEAR; N, NORTH; W, WEST; E, EAST]

 Migration Distance
 Mean Center Mean Center from Previous
Years North Latitude West Longitude Urban Area Center
Mapped (D-M-S) (D-M-S) (meters)

1977 30-20-2 -97-47-28
1992 30-20-29 -97-48-14 1,482
2000 30-20-39 -97-47-35 1,084

 Migration Direction Annual
 from Previous Urban Area Center
Years Urban Area Center Migration Rate
Mapped (bearing: D-M-S) (meters/yr)

1977
1992 N 54-3-28 W 99
2000 N 75-34-45 E 136

Some mapped centers might be obscured where migration distances are
relatively short.

TABLE 4: AUSTIN-ROUND ROCK MSA POPULATION CENTER
MIGRATION METRICS (BLUE PATH IN FIG. 7) [D, DEGREE; M, MINUTE;
S, SECOND; YR, YEAR; N, NORTH; E, EAST]

 Migration Distance
 Mean Center Mean Center from Previous
Years North Latitude West Longitude Population Center
Mapped (D-M-S) (D-M-S) (meters)

1970 30-18-29 -97-45-11
1980 30-19-34 -97-44-56 2,060
1990 30-20-19 -97-44-41 1,423
2000 30-21-7 -97-44-21 1,579

 Projected

2010 30-21-16 -97-44-13 348
2020 30-21-29 -97-44-0 540
2030 30-21-47 -97-43-43 701
2040 30-22-4 -97-43-25 719

 Migration Direction Annual
 from Previous Population Center
Years Population Center Migration Rate
Mapped (bearing: D-M-S) (meters/yr)

1970
1980 N10-27-43E 206
1990 N15-4-17E 142
2000 N19-56-2E 158

 Projected

2010 N32-08-26E 35
2020 N42-25-32E 54
2030 N39-9-33E 70
2040 N40-40-48E 72

Some mapped centers might be obscured where migration distances
are relatively short.

TABLE 5: 16-QUADRANGLE STUDY AREA URBAN-AREA CENTER
MIGRATION METRICS (RED PATH IN FIG. 7) [D, DEGREE; M, MINUTE;
S, SECOND; YR, YEAR; N, NORTH; W, WEST; E, EAST]

 Migration Distance
 Mean Center Mean Center from Previous
Years North Latitude West Longitude Urban Center
Mapped (D-M-S) (D-M-S) (meters)

1983 30-19-14 -97-44-28
1991 30-20-36 -97-45-6 2,705
1997 30-21-30 -97-45-33 1,823
2000 30-22-5 -97-45-56 1,253

 Projected

2010 30-22-29 -97-44-59 1,684
2020 30-22-30 -97-44-43 422
2030 30-22-30 -97-44-43 5
2040 30-22-30 -97-44-43 5

 Migration Direction Annual
 from Previous Urban Area Center
Years Urban Area Center Migration Rate
Mapped (bearing: D-M-S) (meters/yr)

1983
1991 N22-51-25W 338
1997 N23-31-36W 304
2000 N30-51-53W 418

 Projected

2010 N63-59-8E 168
2020 N85-29-01E 42
2030 N81-8-31E 0.5
2040 N80-32-16E 0.5

Some mapped centers might be obscured where migration distances
are relatively short.

TABLE 6: COMMUTING TO AND FROM
THE AUSTIN-ROUND ROCK MSA

Commuter Source/Destination 1970 1980 1990 2000

San Antonio MSA 0 -35 -141 103
Other Texas Counties -498 -589 -973 3,147
United States 0 0 0 -86
International 0 0 0 -58
Elsewhere/Unknown -174 -257 -718 0

TABLE 7: SAN ANTONIO EA POPULATION CENTER OF MASS
MIGRATION METRICS [D, DEGREE; M, MINUTE; S, SECOND; YR, YEAR;
N, NORTH; W, WEST; E, EAST; S, SOUTH]

 Migration Distance
 Mean Center Mean Center from Previous
Years North Latitude West Longitude Population Center
Mapped (D-M-S) (D-M-S) (meters)

1970 29-25-36 -98-37-14
1980 29-25-39 -98-38-23 1,868
1990 29-26-11 -98-37-23 1,869
2000 29-26-25 -98-37-4 667

 Projected

2010 29-26-18 -98-37-8 219
2020 29-26-15 -98-37-10 112
2030 29-26-12 -98-37-13 111
2040 29-26-9 -98-37-17 150

 Migration Direction Annual
 from Previous Population Center
Years Population Center Migration Rate
Mapped (bearing: D-M-S) (meters/yr)

1970
1980 N 85-5-41 W 187
1990 N 60-27-22 E 187
2000 N 51-46-53 E 67

 Projected

2010 S 28-19-10 W 22
2020 S 37-21-49 W 11
2030 S 34-1-17 W 11
2040 S 50-20-8 W 15

Some mapped centers might be obscured where migration distances are
relatively short.

FIGURE 5: COUNTY POPULATION PROJECTIONS

Austin-Round Rock MSA County Population Projections

 1970 1980 1990 2000 2010

Bastrop 17,297 24,726 38,263 57,733 76,195
Caldwell 21,178 23,637 26,392 32,194 40,312
Hays 27,642 40,594 65,614 97,589 140,173
Travis 295,516 419,573 576,407 812,280 963,894
Williamson 37,305 76,521 139,551 249,967 344,892

 2020 2030 2040

Bastrop 99,453 127,344 160,017
Caldwell 50,041 60,192 70,698
Hays 183,847 230,859 280,076
Travis 1,108,849 1,253,626 1,390,858
Williamson 459,222 600,687 761,893
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Author:Sherrouse, Ben C.; Hester, David J.
Publication:Urban and Regional Information Systems Association Annual Conference Proceedings
Article Type:Report
Geographic Code:1U7TX
Date:Jan 1, 2006
Words:4547
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