Cherokee County orecasts Technical Report: An Element of the Joint Comprehensive Plan For Cherokee County and the Cities of Ball Ground, Waleska and Woodstock, Georgia Plan Cherokee Team: ROSS+associates McBride Dale Clarion Day Wilburn Associates Robert Charles Lesser & Company
Technical Report: Forecasts Cherokee County and its Cities Table of Contents Introduction... 1 Regressions... 1 TAZ Data for Cities... 3 Cherokee Forecasts: Methodology... 3 City Forecasts... 4 County Forecasts... 5 Analysis... 5 Appendix A: Trend Regressions... 9 Appendix B: City TAZ Data... 19 Appendix C: Mobility Forecasts... 22 Appendix D: The Data Regression Process... 24 Best Fit Regressions... 24 Trend Projections... 26 List of Tables Cherokee County Regressions against 1970...2 Estimated Growth Rates for Key Cities...3 City Forecasts:...7 County Forecasts:...8 Estimates: U.S. Bureau of the...10 Cherokee County Regressions against 1993...11 Cherokee County Regressions against...11 Ball Ground City Regressions against 1993...12 January i
Technical Report: Forecasts Cherokee County and its cities Ball Ground City Regressions against...12 Canton City Regressions against 1993...13 Canton City Regressions against...13 Holly Springs City Regressions against 1993...14 Holly Springs City Regressions against...14 Nelson City (pt) Regressions against 1993...15 Nelson City (pt) Regressions against...15 Waleska City Regressions against 1993...16 Waleska City Regressions against...16 Woodstock City Regressions against 1993...17 Woodstock City Regressions against...17 Unincorporated Cherokee County Regressions against 1993...18 Unincorporated Cherokee County Regressions against...18 Socioeconomic Data by TAZ...20 Socioeconomic Data by TAZ...21 January ii
Technical Report: Forecasts Cherokee County and its Cities Introduction This report presents the methodology used in preparing population forecasts for Cherokee County and its cities, and contains recommendations for use in the Joint Comprehensive Plan 10thYear Update. The selected population forecasts will become the basis for household and housing unit forecasts, and for other populationrelated tables in the Assessment Report (age breakdowns, etc.). They will also be influential in making employment forecasts. This report contains the following text that presents the methodology and resulting forecasts, and three appendices that contain the population trend line regression data and tables, the Traffic Analysis Zone data tables for the cities, and a brief explanation of the methodology used by the Atlanta Regional Commission in preparing their Mobility Forecasts for the Regional Transportation Plan. Regressions As a first step, 1 st, 2 nd and 3 rd order regressions were prepared for the county as a whole, each of its cities and the unincorporated area against two sets of historic trend data annual population figures for the longer range 1993 period and for the more recent period. In addition, regressions were prepared for the county as a whole covering the 1970 base line period (presented below). The 1 st, 2 nd and 3 rd order regressions produce straight line, parabola and ess curve functions, respectively, projecting the trend line data out to. As noted, both the longer view and the affect of the more immediate past are considered. The first page in the Trend Regressions section (Appendix A, starting on page 9) presents the methodology used to rectify the Bureau's annual population estimates for 1993 through 1999 with the actual census count. As the years go by, Bureau estimates become ever more inaccurate until, when the next decennial census is taken, surprises occur. The top table on the first page of Appendix A (page 10) presents the annual July 1 estimates for all years between 1993 and 1999 (published in October of 1999) and for through (published in July, ). The middle table on the page projects what the census count would have been, had those annual estimates for 19931999 been correct. This figure is compared to the actual census figure 1 and the variance between them is determined. This variance is then applied to the 19931999 estimates (as reported) to modify them to the actual census. The bottom table on the page presents the annual data, as rectified to the census. 1 All figures are the Bureau's estimates of population as of July 1 each year, including for, for data consistency. January 1
Technical Report: Forecasts Cherokee County and its cities The annual population data on that bottom table are used as the historic trend line data in calculating the mathematical regressions and projecting the trends to. The 1993 period was chosen instead of 1990 because it was noticed that a dip in annual estimates occurred across the board between 1992 and 1993, which reflects the recession of the early `90s. This dip would have thrown the regression curves off trying to account for the noncontinuous data stream. Pages are then presented in the Trend Regressions section that show the regression data for each jurisdiction along with a graph of the projections; each jurisdiction's page contains projections against both the 1993 period and the period. As a comparison, countywide data in 5year increments for 1970 2 were also prepared to. The results are: Cherokee County Regressions against 1970 Trend Projections* 1970 31,059 30,765 1975 40,073 40,269 1980 51,699 52,566 1985 68,600 68,425 1990 90,204 88,612 1995 113,497 113,895 143,811 145,042 183,449 182,819 186,321 221,664 227,994 207,660 266,563 281,334 228,998 316,175 343,607 250,336 370,500 415,579 271,675 429,536 498,018 Correlation Coefficients 0.952776 0.999241 0.999725 5 500,000 4 400,000 3 300,000 2 1 1970 1975 1980 1985 1990 1995 2 The data point was drawn from the 1993 2 nd order regression for the county. January 2
Technical Report: Forecasts Cherokee County and its cities TAZ Data for Cities Two tables have been drawn from the forecast data prepared by the Atlanta Regional Commission for the Regional Transportation Plan. The data on the tables are shown for each Traffic Analysis Zone (TAZ) within which a city is located or partially located. The city TAZ data is combined for each of the key cities 3 in the county. The two tables present data for the years and, respectively. (See Appendix B, the City TAZ Data Section, starting on page 19 for the data tables.) After the City TAZ Data Section, the Atlanta Regional Commission s summary of their Mobility forecasting methodology is included as Appendix C. This is the methodology that was used by ARC to produce the TAZ estimates and forecasts. Cherokee Forecasts: Methodology Since Mobility does not provide forecasts for cities, the first step is to consider the expected share of TAZ population that will be located within each city in the future. The following table shows the calculation of growth rates that have been used to forecast population in the county s key cities. (Note that the population figures on the following table are used only in estimating the growth rate; the actual forecasts are discussed in the next section City Forecasts.) Estimated Growth Rates for Key Cities TAZ * % of TAZ in % of TAZ in (est**) TAZ * City at % City at % Annual Rate of Increase at % Ball Ground 3,043 730 23.99% 80.00% 10,727 2,573 8,582 8.561% Canton 13,531 7,709 56.97% 80.00% 49,179 28,019 39,343 5.583% Holly Springs 7,577 3,195 42.17% 66.67% 23,328 9,837 15,553 5.417% Waleska 3,130 616 19.68% 25.00% 8,979 1,767 2,245 4.405% Woodstock 27,101 10,050 37.08% 85.00% 51,653 19,155 43,905 5.038% * Source: Atlanta Regional Commission, Regional Transportation Plan, for those TAZs including and surrounding each city indicated. ** percentage empiracally chosen relative to "most likely" regression projection. 3 The city forecast methodology differs from all of the other cities for the portions of Mt. Park and Nelson in the county, so these cities are not shown on the tables. January 3
Technical Report: Forecasts Cherokee County and its cities figures for, taken from the data tables for the TAZs that include and surround each city, are shown on the above table, along with each city s population count from the census. 4 This yields the percentage of the population in each TAZ grouping that actually lived in each city at that time. The fourth column on the table above shows the estimated percentage of the city TAZ population that is expected to be living within each city in. These two percentages ( actual and projected) are applied to the city TAZ population that is forecast to, yielding first an estimated city population if the city s share of the TAZ population does not increase (the % ), and secondly the population anticipated within the city assuming an increase in share (the % ), at least within the TAZs identified as currently including and surrounding each city. The last column contains the average annual growth rate that each city will have experienced between and in population increase within those identified city TAZs, assuming an increase in city share of the total population over time (the % ). 5 The increase in share results from continued annexation as well as attraction of infill development from within the city TAZ groupings. As will be seen below, the forecast methodologies for the cities of Canton, Holly Springs and Woodstock anticipate further expansion of the cities beyond the identified city TAZs such that the total forecast for each city is greater than the city population shown on the table above. Ball Ground and Waleska are located within large city TAZ groups such that expansion into neighboring TAZs is not expected. City Forecasts The first table on the page following this methodology text (see page 7) presents the calculations that represent the recommended population forecasts for each city (or portion of a city) in the county. For the key cities Ball Ground, Canton, Holly Springs, Waleska and Woodstock the annual rate of increase using the % from the table above is applied to the population (as estimated by the Bureau) and to the resulting population each subsequent year, ending in. 6 Mt. Park and Nelson, which have only minor portions of their city limits in the county, are treated somewhat differently. In the case of Mt. Park, estimates have shown a consistent population of 13 every year since ; we have assumed that this will continue into the foreseeable future. For Nelson, we selected the 2 nd order (parabolic) trend line projection calculated against the estimates; 7 the average annual rate of population increase shown on the table on page 7 was calculated from the and projected figures for comparison to the other cities. 4 TAZ data reflect actual counts from the, not the July 1 estimates. 5 The percentages were estimated, in part, with reference to most likely projections generated by the regressions, presented later in this report. 6 Over the forecast period, of course, individual years will experience a higher or lower result than that forecast because an average rate is applied to each year. By, however, the forecast will be accurate in the aggregate. 7 The same total for all cities is used in both methodologies because the city forecasts were prepared independently from the countywide forecasts and as such stand on their own. January 4
Technical Report: Forecasts Cherokee County and its cities County Forecasts County population forecasts are shown on the table and graphs on the page following the city forecasts (see page 8). Three methodologies are illustrated on the page: use of the ARC Mobility figures for the county as a whole for the low forecast, and consideration of medium and high countywide figures drawn from the trend line regressions. In each methodology, the total population forecast for the cities is subtracted from the county total to estimate the population each year in the unincorporated area. The Atlanta Regional Commission s Mobility forecasts a population for Cherokee County of 362,414. 8 This forecast is combined with the Bureau s population estimate to identify the resulting average annual rate of increase for the county as a whole. Applying the average annual rate to each year produces an annual population for the county. By subtracting the annual population forecast for the cities as a group, the remaining population will be located within unincorporated areas of the county. The average annual rate of increase is calculated for the unincorporated population growth () and shown for comparison on the table. The ARC Mobility forecast is roughly consistent with several of the trend line projections calculated for the county as a whole, and included in the Trend Regressions section of this report (Appendix A). For the medium forecast shown on the County table below, the 3 rd order ( ess curve) trend line projection calculated against the historic population estimates from 1993 is used as a most likely forecast. The high population forecast represents the 2 nd order (parabola) trend line projection and is essentially an unconstrained forecast. As in the first methodology, the city population totals are subtracted from the county total to yield the population forecast in the unincorporated area. Analysis All of the methodologies used for the countywide population forecasts reflect an increasing share of the population located in one or another city most notably Canton, Holly Springs and Woodstock each of which is anticipated to roughly quadruple their population. Using the ARC Mobility forecast for the county (the low forecast), by the share of the countywide population living within all of the cities combined will have grown from 22% in to 41% in. If the medium countywide population forecast is considered, the total share among the cities still grows to 36%, while the high forecast results in an allcities share of 29% (still an increase over ). Differences, however, can be seen between the low and the high forecasts that are most notably evident in the growth rate and pattern for the unincorporated area. Under the Mobility scenario, the countywide population continues to increase at an increasing rate (note the upward curve in the line on the first graph). With the comparably higher rate of growth in population located within the cities, the unincorporated population grows at a much lower, but steady, rate (note the flatness of the line on the first graph). 8 A summary of ARC s methodology is attached as Appendix C. January 5
Technical Report: Forecasts Cherokee County and its cities Considering the medium forecast, however, the countywide total increases at a steady rate (a function of using an average annual rate of growth), but the unincorporated population exhibits a much stronger ess curve shape, suggesting a continuation of an increasing growth rate over the next 10 years or so, then dropping off in the latter part of the forecast period still growing but at a decreasing annual rate. Ultimately, under the medium scenario, the unincorporated population in will be higher than under the low scenario, but the pattern of that increase could be characterized as a higher rate of growth in the coming decade that drops off in time, compared to a steady state of growth throughout the forecast period, respectively. In the "high" forecast, growth in the unincorporated area continues at a steady but everincreasing rate. This forecast is considered "unconstrained" by the naturalgrowth effects of dwindling land resources, increasing land prices, and market forces. The reoccurring theme among all of these regressions, based on the 1993 base period, is a medium population forecast in the low 400,000s and a high forecast in the low 500,000s. Although we believe the 500,000s will not be achieved by because of all the natural growth processes that are evident in the medium forecast, such a high estimate is presented for discussion and may represent the initial buildout of the county after. January 6
City Forecasts: Ball Ground Canton Holly Springs Mt. Park (pt) Nelson (pt) Waleska Woodstock All Cities Total Rate: 8.561% 5.583% 5.417% n/a 4.288% 4.405% 5.038% n/a 70,000 791 15,094 4,699 13 319 726 17,214 38,856 859 15,937 4,954 13 329 758 18,081 40,931 933 16,827 5,222 13 341 791 18,992 43,119 1,013 17,767 5,505 13 354 826 19,949 45,427 1,100 18,759 5,803 13 369 862 20,954 47,860 1,194 19,806 6,117 13 385 900 22,010 50,425 1,296 20,912 6,448 13 402 940 23,119 53,130 1,407 22,080 6,797 13 420 981 24,284 55,982 1,527 23,313 7,165 13 440 1,024 25,507 58,989 1,658 24,615 7,553 13 461 1,069 26,792 62,161 1,800 25,989 7,962 13 483 1,116 28,142 65,505 1,954 27,440 8,393 13 507 1,165 29,560 69,032 2,121 28,972 8,848 13 532 1,216 31,049 72,751 2,303 30,590 9,327 13 558 1,270 32,613 76,674 2,500 32,298 9,832 13 585 1,326 34,256 80,810 2,714 34,101 10,365 13 614 1,384 35,982 85,173 2,946 36,005 10,926 13 644 1,445 37,795 89,774 3,198 38,015 11,518 13 675 1,509 39,699 94,627 3,472 40,138 12,142 13 708 1,575 41,699 99,747 3,769 42,379 12,800 13 742 1,644 43,800 105,147 4,092 44,745 13,493 13 777 1,716 46,006 110,842 4,442 47,243 14,224 13 813 1,792 48,324 116,851 4,822 49,881 14,995 13 851 1,871 50,758 123,191 5,235 52,666 15,807 13 890 1,953 53,315 129,879 5,683 55,607 16,663 13 930 2,039 56,001 136,936 6,170 58,712 17,566 13 972 2,129 58,822 144,384 6,698 61,990 18,518 13 1,015 2,223 61,785 152,242 60,000 40,000 30,000 Notes: population figures: U.S. Bureau of the annual estimates, as of July 1 each year. population figures for Ball Ground, Canton, Holly Springs, Waleska and Woodstock based on average annual rate of increase for each city. 20,000 population figures for the portion of Mt. Park in Cherokee County assumes a continuation of current population. population figures for the portion of Nelson in Cherokee County based on 2nd order (parabolic) trend line regression against historic data. 10,000 Ball Ground Canton Holly Springs Waleska Woodstock January 7
County Forecasts: All Cities Total LOW FORECAST County Uninc. Total County MEDIUM FORECAST County Uninc. Total County HIGH FORECAST County Uninc. Total County n/a 2.847% 1.693% 3.410% 2.610% 4.288% 3.910% 5 38,856 174,680 135,824 174,680 135,824 174,680 135,824 40,931 179,653 138,722 183,449 142,518 183,908 142,976 43,119 184,767 141,648 192,107 148,988 192,989 149,870 45,427 190,027 144,600 200,979 155,551 202,435 157,008 47,860 195,437 147,577 210,044 162,184 212,247 164,386 50,425 201,001 150,576 219,283 168,858 222,423 171,998 53,130 206,723 153,593 228,675 175,545 232,964 179,834 55,982 212,608 156,626 238,200 182,218 243,870 187,887 58,989 218,661 159,672 247,838 188,849 255,141 196,151 62,161 224,886 162,725 257,569 195,408 266,776 204,615 65,505 231,288 165,783 267,372 201,867 278,777 213,272 69,032 237,872 168,840 277,228 208,196 291,143 222,111 72,751 244,644 171,893 287,116 214,366 303,873 231,122 76,674 251,609 174,935 297,017 220,343 316,969 240,295 80,810 258,772 177,962 306,909 226,099 330,429 249,619 85,173 266,139 180,966 316,773 231,600 344,254 259,081 89,774 273,715 183,941 326,589 236,815 358,445 268,670 94,627 281,507 186,880 336,336 241,709 373,000 278,372 99,747 289,521 189,774 345,995 246,248 387,920 288,173 105,147 297,763 192,616 355,545 250,398 403,205 298,058 110,842 306,240 195,398 364,966 254,124 418,855 308,013 116,851 314,958 198,107 374,238 257,386 434,869 318,018 123,191 323,924 200,733 383,340 260,149 451,249 328,058 129,879 333,146 203,267 392,253 262,374 467,994 338,115 136,936 342,630 205,694 400,957 264,020 485,103 348,167 144,384 352,384 208,000 409,430 265,046 502,578 358,194 152,242 362,414 210,172 417,654 265,412 520,417 368,175 Notes: Low Forecast based on ARC Mobility, Atlanta Regional Commission, forecast for Cherokee County. Calculated annual rate of increase for applied to intervening years. Medium Forecast reflects 3rd order ("ess" curve") trend line regression for Cherokee County against 1993 historic data. Medium Forecast Low Forecast 500,000 4 400,000 3 300,000 2 1 5 500,000 4 400,000 3 300,000 2 1 County Total Uninc. County All Cities Total County Total Uninc. County All Cities Total High Forecast reflects 2nd order (parabola) trend line regression for Cherokee County against 1993 historic data. All figures for Unincorporated Cherokee County calculated by subtracting All City from Total County. 5 500,000 High Forecast 4 400,000 3 300,000 2 1 County Total Uninc. County All Cities Total January 8
Appendix A: Trend Regressions January 9
Estimates: U.S. Bureau of the Cherokee County and Its Cities: 1993 Bureau Annual Estimates (7/1 of each year) Estimated (by ) Area Name 1993 1994 1995 1996 1997 1998 1999 Cherokee County, GA 103,226 108,930 114,743 121,187 127,110 134,352 141,686 143,811 151,703 159,556 166,947 174,680 Ball Ground city, GA 1,034 1,095 1,159 1,227 1,288 1,353 1,416 734 751 767 779 791 Canton city, GA 5,826 5,842 5,881 5,889 5,974 6,178 6,786 8,185 9,564 11,372 13,249 15,094 Holly Springs city, GA 2,734 2,940 3,173 3,299 3,338 3,409 3,489 3,600 4,090 4,201 4,409 4,699 Mountain Park city (pt.), GA 18 18 18 20 20 21 21 13 13 13 13 13 Nelson city (pt.), GA 74 79 84 89 93 98 103 288 295 301 308 319 Waleska city, GA 679 700 720 743 762 783 803 619 731 711 718 726 Woodstock city, GA 5,431 5,618 5,854 6,133 6,552 7,621 8,629 10,342 11,502 13,166 14,852 17,214 Balance of Cherokee County, GA 87,430 92,638 97,854 103,787 109,083 114,889 120,439 120,030 124,757 129,025 132,619 135,824 19931999 Annual Estimates Projected to Yr 1993 1994 1995 1996 1997 1998 1999 Divergence Cherokee County, GA 103,291 108,866 114,742 120,935 127,463 134,343 141,594 149,237 0.9636 Ball Ground city, GA 1,040 1,096 1,155 1,218 1,284 1,353 1,426 1,503 0.4884 Canton city, GA 5,678 5,798 5,921 6,046 6,173 6,304 6,437 6,573 1.2453 Holly Springs city, GA 2,839 2,951 3,067 3,187 3,312 3,442 3,577 3,718 0.9683 Mountain Park city (pt.), GA 18 18 19 19 20 21 21 22 0.5917 Nelson city (pt.), GA 75 79 83 88 93 98 104 109 2.6307 Waleska city, GA 681 700 720 740 761 783 805 828 0.7476 Woodstock city, GA 5,156 5,560 5,995 6,465 6,971 7,517 8,106 8,741 1.1831 Balance of Cherokee County, GA 87,804 92,664 97,782 103,172 108,848 114,825 121,118 127,743 0.9396 Annual Estimates Rectified to Estimated (by ) 1993 1994 1995 1996 1997 1998 1999 Cherokee County, GA 103,226 108,364 113,551 119,299 124,469 130,863 137,270 143,811 151,703 159,556 166,947 174,680 Ball Ground city, GA 1,034 1,015 990 958 911 859 795 734 751 767 779 791 Canton city, GA 5,826 6,001 6,336 6,681 7,039 7,408 7,790 8,185 9,564 11,372 13,249 15,094 Holly Springs city, GA 2,734 2,927 3,144 3,254 3,278 3,332 3,394 3,600 4,090 4,201 4,409 4,699 Mountain Park city (pt.), GA 18 17 16 17 15 15 14 13 13 13 13 13 Nelson city (pt.), GA 74 97 123 151 180 212 247 288 295 301 308 319 Waleska city, GA 679 675 668 663 652 642 629 619 731 711 718 726 Woodstock city, GA 5,431 5,765 6,160 6,614 7,238 8,618 9,984 10,342 11,502 13,166 14,852 17,214 Balance of Cherokee County, GA 87,430 91,867 96,114 100,961 105,156 109,777 114,417 120,030 124,757 129,025 132,619 135,824 Sources: U.S. Bureau of the, Annual Estimates and ; projections and rectification to by ROSS+associates. January 10
Cherokee County Regressions against 1993 Trend Projections* 1993 103,226 103,561 1994 108,270 108,082 1995 113,352 113,058 1996 118,984 118,471 1997 124,029 124,298 1998 130,281 130,520 1999 136,535 137,118 143,811 144,070 151,703 151,357 159,556 158,959 166,947 166,855 174,680 175,025 178,373 183,908 183,449 184,900 192,989 192,107 191,427 202,435 200,979 197,954 212,247 210,044 204,481 222,423 219,283 211,008 232,964 228,675 217,535 243,870 238,200 224,062 255,141 247,838 230,589 266,776 257,569 237,116 278,777 267,372 243,643 291,143 277,228 250,170 303,873 287,116 256,697 316,969 297,017 263,224 330,429 306,909 269,750 344,254 316,773 276,277 358,445 326,589 282,804 373,000 336,336 289,331 387,920 345,995 295,858 403,205 355,545 302,385 418,855 364,966 308,912 434,869 374,238 315,439 451,249 383,340 321,966 467,994 392,253 328,493 485,103 400,957 335,020 502,578 409,430 341,547 520,417 417,654 5 500,000 4 400,000 3 300,000 2 1 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.992473 0.999712 0.999733 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Cherokee County Regressions against Trend Projections* 143,811 143,943 151,703 151,641 159,556 159,339 166,947 167,038 174,680 174,736 182,434 182,044 182,577 190,132 189,352 190,952 197,830 196,549 199,978 205,529 203,634 209,845 213,227 210,608 220,743 220,925 217,471 232,863 228,623 224,222 246,396 236,321 230,861 261,532 244,020 237,390 278,461 251,718 243,806 297,375 259,416 250,112 318,463 267,114 256,306 341,916 274,812 262,388 367,925 282,511 268,359 396,680 290,209 274,219 428,371 297,907 279,967 463,190 305,605 285,604 501,326 313,303 291,129 542,970 321,002 296,543 588,313 328,700 301,846 637,545 336,398 307,037 690,856 344,096 312,116 748,437 351,794 317,084 810,479 359,493 321,941 877,172 367,191 326,687 948,707 374,889 331,320 1,025,274 Correlation Coefficients 0.999866 0.999939 0.999964 1, 1,000,000 800,000 600,000 400,000 * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 11
Ball Ground City Regressions against 1993 Trend Projections* 1993 1,034 1,075 1994 1,015 1,017 1995 990 964 1996 958 918 1997 911 877 1998 859 843 1999 795 815 734 794 751 778 767 769 779 765 791 768 684 777 890 656 792 1,009 628 814 1,171 600 841 1,381 572 875 1,644 544 915 1,966 516 961 2,350 488 1,013 2,803 460 1,071 3,328 432 1,136 3,931 404 1,206 4,616 377 1,283 5,390 349 1,366 6,256 321 1,455 7,219 293 1,551 8,285 265 1,652 9,459 237 1,760 10,745 209 1,873 12,148 181 1,993 13,673 153 2,119 15,326 125 2,252 17,111 97 2,390 19,032 69 2,535 21,096 41 2,685 23,307 13 2,842 25,670 (14) 3,005 28,189 30,000 25,000 20,000 15,000 10,000 5,000 (5,000) 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.826202 0.91 0.978159 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Ball Ground City Regressions against Trend Projections* 734 734 751 751 767 766 779 779 791 791 807 800 801 821 807 811 835 812 821 850 816 832 864 817 843 878 816 856 892 813 871 906 808 889 921 802 909 935 793 933 949 782 961 963 769 994 977 754 1,031 992 738 1,074 1,006 719 1,123 1,020 698 1,179 1,034 675 1,241 1,048 650 1,311 1,063 624 1,389 1,077 595 1,476 1,091 564 1,571 1,105 531 1,676 1,119 496 1,791 1,134 460 1,917 1,148 421 2,053 1,162 380 2,201 2,500 2,000 1,500 1,000 500 Correlation Coefficients 0.992714 0.999606 0.999655 * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 12
Canton City Regressions against 1993 Trend Projections* 1993 5,826 6,300 1994 6,001 6,072 1995 6,336 6,045 1996 6,681 6,217 1997 7,039 6,589 1998 7,408 7,161 1999 7,790 7,932 8,185 8,904 9,564 10,075 11,372 11,446 13,249 13,017 15,094 14,787 13,727 16,757 18,204 14,499 18,927 21,709 15,270 21,297 25,890 16,042 23,867 30,812 16,813 26,636 36,538 17,585 29,605 43,131 18,357 32,774 50,655 19,128 36,143 59,173 19,900 39,712 68,750 20,671 43,480 79,447 21,443 47,448 91,331 22,214 51,616 104,463 22,986 55,984 118,907 23,758 60,551 134,727 24,529 65,318 151,987 25,301 70,285 170,750 26,072 75,452 191,079 26,844 80,819 213,039 27,615 86,385 236,692 28,387 92,151 262,103 29,159 98,117 289,335 29,930 104,283 318,451 30,702 110,648 349,516 31,473 117,214 382,592 32,245 123,979 417,743 33,016 130,944 455,033 500,000 4 400,000 3 300,000 2 1 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.84966 0.98259 0.99557 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Canton City Regressions against Trend Projections* 8,185 7,992 9,564 9,743 11,372 11,493 13,249 13,243 15,094 14,993 16,744 17,244 16,599 18,494 19,495 17,559 20,244 21,889 17,740 21,995 24,426 16,911 23,745 27,105 14,843 25,495 29,928 11,304 27,246 32,894 6,064 28,996 36,003 (1,108) 30,746 39,255 (10,441) 32,496 42,649 (22,167) 34,247 46,187 (36,516) 35,997 49,868 (53,719) 37,747 53,692 (74,005) 39,498 57,659 (97,606) 41,248 61,768 (124,752) 42,998 66,021 (155,674) 44,749 70,417 (190,601) 46,499 74,956 (229,765) 48,249 79,638 (273,396) 49,999 84,462 (321,725) 51,750 89,430 (374,981) 53,500 94,541 (433,396) 55,250 99,795 (497,200) 57,001 105,192 (566,624) 58,751 110,731 (641,897) 60,501 116,414 (723,251) Correlation Coefficients 0.99695 0.99928 0.99997 () () (300,000) (400,000) (500,000) (600,000) (700,000) (800,000) * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 13
Holly Springs City Regressions against 1993 Trend Projections* 1993 2,734 2,856 1994 2,927 2,923 1995 3,144 3,010 1996 3,254 3,116 1997 3,278 3,243 1998 3,332 3,389 1999 3,394 3,556 3,600 3,742 4,090 3,948 4,201 4,174 4,409 4,420 4,699 4,686 4,669 4,971 5,161 4,836 5,277 5,642 5,002 5,602 6,206 5,168 5,948 6,860 5,335 6,313 7,614 5,501 6,698 8,475 5,667 7,103 9,453 5,833 7,528 10,554 6,000 7,973 11,788 6,166 8,438 13,164 6,332 8,923 14,688 6,499 9,427 16,371 6,665 9,952 18,219 6,831 10,496 20,242 6,998 11,060 22,447 7,164 11,645 24,844 7,330 12,249 27,440 7,496 12,873 30,244 7,663 13,517 33,265 7,829 14,180 36,509 7,995 14,864 39,987 8,162 15,568 43,706 8,328 16,291 47,675 8,494 17,035 51,901 8,660 17,798 56,394 8,827 18,581 61,161 70,000 60,000 40,000 30,000 20,000 10,000 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.939196 0.970579 0.975911 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Holly Springs City Regressions against Trend Projections* 3,600 3,696 4,090 3,948 4,201 4,200 4,409 4,452 4,699 4,703 4,955 4,803 5,449 5,207 4,904 6,840 5,458 4,961 9,110 5,710 4,974 12,488 5,962 4,944 17,207 6,213 4,872 23,496 6,465 4,755 31,586 6,717 4,596 41,706 6,969 4,393 54,089 7,220 4,147 68,964 7,472 3,858 86,561 7,724 3,525 107,112 7,975 3,149 130,846 8,227 2,730 157,995 8,479 2,267 188,788 8,730 1,761 223,456 8,982 1,212 262,231 9,234 620 305,341 9,486 (16) 353,018 9,737 (695) 405,492 9,989 (1,417) 462,995 10,241 (2,182) 525,755 10,492 (2,991) 594,004 10,744 (3,843) 667,972 10,996 (4,739) 747,890 11,247 (5,677) 833,988 Correlation Coefficients 0.952986 0.962851 0.994819 900,000 800,000 700,000 600,000 500,000 400,000 300,000 0 * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 14
Nelson City (pt) Regressions against 1993 Trend Projections* 1993 74 83 1994 97 107 1995 123 132 1996 151 156 1997 180 180 1998 212 204 1999 247 228 288 253 295 277 301 301 308 325 319 349 374 335 297 398 342 268 422 346 223 446 347 162 470 346 82 494 343 (18) 519 336 (141) 543 328 (287) 567 317 (458) 591 303 (657) 615 287 (884) 640 268 (1,142) 664 247 (1,432) 688 223 (1,756) 712 197 (2,116) 736 168 (2,513) 761 136 (2,948) 785 103 (3,425) 809 66 (3,944) 833 27 (4,507) 857 (14) (5,116) 882 (58) (5,772) 906 (105) (6,478) 930 (154) (7,234) 954 (205) (8,043) 978 (259) (8,906) 2,000 (2,000) (4,000) (6,000) (8,000) (10,000) 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.959849 0.984246 0.994862 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Nelson City (pt) Regressions against Trend Projections* 288 288 295 294 301 301 308 309 319 318 325 329 336 332 341 362 340 354 399 347 369 451 355 385 518 362 402 604 370 420 711 377 440 843 385 461 1,000 392 483 1,186 400 507 1,404 407 532 1,655 415 558 1,943 422 585 2,269 430 614 2,637 437 644 3,049 445 675 3,506 452 708 4,013 460 742 4,571 467 777 5,183 475 813 5,850 482 851 6,577 490 890 7,365 497 930 8,217 505 972 9,135 512 1,015 10,122 12,000 10,000 8,000 6,000 4,000 2,000 0 Correlation Coefficients 0.985459 0.995595 0.999975 * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 15
Waleska City Regressions against 1993 Trend Projections* 1993 679 1994 675 1995 668 1996 663 1997 652 1998 642 1999 629 619 731 711 718 726 709 773 764 714 807 791 719 846 820 724 889 849 729 936 880 734 987 911 739 1,043 942 744 1,103 972 749 1,167 1,002 754 1,235 1,031 759 1,307 1,059 764 1,384 1,085 769 1,465 1,109 774 1,550 1,130 779 1,639 1,149 784 1,733 1,164 789 1,830 1,176 794 1,932 1,184 799 2,039 1,188 804 2,149 1,187 809 2,263 1,181 814 2,382 1,170 819 2,505 1,154 824 2,633 1,131 829 2,764 1,102 834 2,900 1,066 3,500 3,000 2,500 2,000 1,500 1,000 500 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.225123 0.596730 0.599341 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Waleska City Regressions against Trend Projections* 619 661 731 681 711 701 718 721 726 741 761 671 857 781 600 1,159 802 504 1,701 822 382 2,550 842 234 3,772 862 60 5,433 882 (139) 7,601 902 (365) 10,342 922 (616) 13,721 942 (894) 17,806 962 (1,197) 22,663 982 (1,526) 28,359 1,003 (1,881) 34,960 1,023 (2,261) 42,533 1,043 (2,668) 51,144 1,063 (3,100) 60,860 1,083 (3,558) 71,746 1,103 (4,043) 83,870 1,123 (4,553) 97,299 1,143 (5,088) 112,098 1,163 (5,650) 128,334 1,183 (6,238) 146,074 1,204 (6,851) 165,384 1,224 (7,490) 186,331 1,244 (8,155) 208,980 1,264 (8,846) 233,400 Correlation Coefficients 0.467712 0.738617 0.943398 2 1 () * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 16
Woodstock City Regressions against 1993 Trend Projections* 1993 5,431 5,482 1994 5,765 5,738 1995 6,160 6,149 1996 6,614 6,716 1997 7,238 7,439 1998 8,618 8,317 1999 9,984 9,350 10,342 10,539 11,502 11,883 13,166 13,383 14,852 15,039 17,214 16,850 16,458 18,816 19,236 17,491 20,939 21,745 18,525 23,216 24,547 19,558 25,649 27,662 20,591 28,238 31,108 21,625 30,982 34,902 22,658 33,882 39,064 23,692 36,937 43,612 24,725 40,148 48,564 25,758 43,514 53,939 26,792 47,036 59,755 27,825 50,714 66,030 28,859 54,546 72,783 29,892 58,535 80,033 30,925 62,679 87,798 31,959 66,978 96,096 32,992 71,433 104,945 34,026 76,044 114,365 35,059 80,810 124,373 36,093 85,731 134,988 37,126 90,808 146,229 38,159 96,041 158,113 39,193 101,429 170,660 40,226 106,973 183,887 41,260 112,672 197,813 42,293 118,527 212,457 2 1 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.944248 0.994151 0.994826 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Woodstock City Regressions against Trend Projections* 10,342 10,343 11,502 11,533 13,166 13,069 14,852 14,951 17,214 17,181 18,543 19,756 19,997 20,253 22,679 23,401 21,962 25,948 27,496 23,672 29,563 32,367 25,381 33,525 38,101 27,090 37,834 44,783 28,800 42,489 52,500 30,509 47,491 61,337 32,219 52,840 71,381 33,928 58,535 82,718 35,637 64,576 95,433 37,347 70,964 109,613 39,056 77,699 125,343 40,766 84,780 142,710 42,475 92,208 161,799 44,184 99,982 182,697 45,894 108,103 205,490 47,603 116,571 230,263 49,313 125,385 257,103 51,022 134,546 286,095 52,731 144,053 317,326 54,441 153,907 350,881 56,150 164,107 386,847 57,860 174,654 425,310 59,569 185,548 466,355 61,278 196,788 510,069 Correlation Coefficients 0.985106 0.999279 0.999378 600,000 500,000 400,000 300,000 0 * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 17
Unincorporated Cherokee County Regressions against 1993 Trend Projections* 1993 87,430 86,926 1994 91,867 91,708 1995 96,114 96,442 1996 100,961 101,127 1997 105,156 105,762 1998 109,777 110,349 1999 114,417 114,886 120,030 119,375 124,757 123,814 129,025 128,204 132,619 132,546 135,824 136,838 141,825 141,082 138,848 146,363 145,276 140,980 150,900 149,421 142,327 155,438 153,518 142,790 159,975 157,565 142,272 164,513 161,563 140,673 169,050 165,513 137,897 173,587 169,413 133,843 178,125 173,264 128,416 182,662 177,066 121,515 187,200 180,820 113,044 191,737 184,524 102,903 196,275 188,179 90,995 200,812 191,785 77,222 205,350 195,342 61,484 209,887 198,850 43,685 214,425 202,310 23,726 218,962 205,720 1,508 223,500 209,081 (23,066) 228,037 212,393 (50,095) 232,575 215,656 (79,676) 237,112 218,870 (111,909) 241,650 222,035 (146,891) 246,187 225,151 (184,720) 250,725 228,218 (225,495) 255,262 231,236 (269,314) 300,000 () () (300,000) 1993 1994 1995 1996 1997 1998 1999 Correlation Coefficients 0.998252 0.998524 0.999575 * Projections based on 1st, 2nd and 3rd order regressions against 1993 estimates, as rectified to the by ROSS+associates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. Unincorporated Cherokee County Regressions against Trend Projections* 120,030 120,561 124,757 124,506 129,025 128,451 132,619 132,396 135,824 136,341 140,286 138,427 138,525 144,231 140,513 140,807 148,176 142,068 142,698 152,121 143,092 144,233 156,066 143,584 145,446 160,011 143,546 146,374 163,956 142,976 147,050 167,901 141,875 147,510 171,846 140,243 147,789 175,791 138,080 147,922 179,736 135,386 147,944 183,681 132,160 147,889 187,626 128,404 147,794 191,571 124,116 147,692 195,516 119,297 147,619 199,461 113,947 147,610 203,406 108,066 147,700 207,351 101,654 147,924 211,296 94,710 148,316 215,241 87,236 148,913 219,186 79,230 149,748 223,131 70,693 150,857 227,076 61,625 152,275 231,021 52,026 154,037 234,966 41,896 156,178 238,911 31,234 158,732 Correlation Coefficients 0.993670 0.999974 0.999977 300,000 2 1 0 * Projections based on 1st, 2nd and 3rd order regressions against estimates. Sources: U.S. Bureau of the, Annual Estimates and ; projections by ROSS+associates. January 18
Appendix B: City TAZ Data January 19
Socioeconomic Data by TAZ Construction Manufacturing TCU Wholesale Retail Fire Service Total Private Government Government Total Households University Enrollment Acre City TAZ Ball Ground 1468 54 44 14 35 18 10 8 183 6 6 189 907 324 4,916 Ball Ground 1469 41 64 16 20 21 14 28 204 84 84 288 2,136 776 20,757 Ball Ground 95 108 30 55 39 24 36 387 90 90 477 3,043 1,100 25,673 Canton 1481 4 1 1 4 3 13 13 452 150 4,325 Canton 1490 62 6 3 1,279 49 1,148 2,547 88 88 2,635 2,871 1,062 5,398 Canton 1491 19 1 7 376 13 147 563 344 344 907 466 195 531 Canton 1503 134 4 11 149 149 721 246 793 Canton 1504 20 97 733 3 73 926 2 2 928 864 307 385 Canton 1505 171 46 16 64 305 169 182 953 9 9 962 1,058 459 1,243 Canton 1506 39 35 98 35 1 20 228 231 231 459 1,870 616 3,004 Canton 1507 20 56 38 140 44 86 810 1,194 1,370 1,370 2,564 2,405 807 2,123 Canton 1508 3 589 287 8 46 933 296 296 1,229 1,392 517 2,745 Canton 1510 76 8 6 143 8 30 271 271 1,432 512 2,125 Canton 414 832 171 530 3,024 336 2,470 7,777 2,340 2,340 10,117 13,531 4,871 22,672 Holly Springs 1512 16 6 8 1 3 21 55 55 1,897 635 2,310 Holly Springs 1514 209 540 13 41 4 8 59 874 83 83 957 2,016 743 1,556 Holly Springs 1515 62 320 16 52 1 21 472 472 1,097 376 1,021 Holly Springs 1516 131 331 90 14 3 99 668 668 2,567 876 1,371 Holly Springs 418 1,197 37 184 18 15 200 2,069 83 83 2,152 7,577 2,630 6,258 Waleska 1474 4 23 7 15 49 4 4 53 466 165 1,104 2,689 Waleska 1475 126 2 25 1 211 365 30 30 395 615 220 3,119 Waleska 1477 24 9 6 7 46 4 4 50 1,000 329 10,855 Waleska 1478 20 8 16 25 69 70 70 139 1,049 380 6,125 Waleska 174 25 17 47 8 258 529 108 108 637 3,130 1,094 1,104 22,788 Woodstock 1513 16 12 28 28 512 191 906 Woodstock 1529 22 57 48 20 71 218 218 999 400 735 Woodstock 1531 7 19 14 132 34 75 281 12 12 293 2,418 990 740 Woodstock 1532 20 5 12 5 10 52 2 2 54 1,449 506 930 Woodstock 1533 28 39 8 138 13 109 335 71 71 406 852 303 989 Woodstock 1534 58 4 1 209 20 254 546 24 24 570 1,027 423 411 Woodstock 1535 19 1 47 13 101 181 7 7 188 361 144 233 Woodstock 1536 21 1 8 89 37 162 318 14 14 332 1,971 662 743 Woodstock 1537 120 451 65 222 194 41 232 1,325 48 48 1,373 723 273 1,323 Woodstock 1538 38 35 39 42 704 107 539 1,504 151 151 1,655 788 354 518 Woodstock 1539 48 4 23 59 349 124 190 797 30 30 827 766 280 415 Woodstock 1541 192 4 2 66 700 74 394 1,432 18 18 1,450 2,181 762 870 Woodstock 1545 14 3 11 231 46 366 671 13 13 684 6,030 2,020 2,418 Woodstock 1546 131 8 43 369 71 296 918 426 426 1,344 7,024 2,557 1,811 Woodstock 734 533 165 536 3,222 605 2,811 8,606 816 816 9,422 27,101 9,865 13,042 Source: Atlanta Regional Commission. January 20
Socioeconomic Data by TAZ Construction Manufacturing TCU Wholesale Retail Fire Service Total Private Government Government Total Households University Enrollment Acre City TAZ Ball Ground 1468 169 22 52 18 144 52 86 543 35 35 578 2,838 1,019 4,916 Ball Ground 1469 236 36 90 12 315 126 356 1,171 275 275 1,446 7,889 3,089 20,757 Ball Ground 405 58 142 30 459 178 442 1,714 310 310 2,024 10,727 4,108 25,673 Canton 1481 32 25 7 31 63 50 65 273 20 20 293 2,144 780 4,325 Canton 1490 130 205 53 153 4,182 361 2,823 7,907 84 84 7,991 9,795 3,599 5,398 Canton 1491 32 16 22 9 888 63 328 1,358 288 288 1,646 1,595 623 531 Canton 1503 16 1 22 3 429 32 49 552 1 1 553 2,189 898 793 Canton 1504 58 82 11 2 1,813 20 191 2,177 3 3 2,180 3,279 1,030 385 Canton 1505 423 37 92 123 922 472 482 2,551 15 15 2,566 3,882 1,633 1,243 Canton 1506 191 34 455 86 654 130 200 1,750 288 288 2,038 6,268 2,428 3,004 Canton 1507 83 69 211 240 205 120 2,080 3,008 1,874 1,874 4,882 8,681 3,170 2,123 Canton 1508 24 686 59 484 62 3 227 1,545 439 439 1,984 6,579 2,464 2,745 Canton 1510 197 19 41 94 724 182 337 1,594 62 62 1,656 4,767 1,834 2,125 Canton 1,186 1,174 973 1,225 9,942 1,433 6,782 22,715 3,074 3,074 25,789 49,179 18,459 22,672 Holly Springs 1512 51 16 42 88 83 95 248 623 49 49 672 5,470 2,104 2,310 Holly Springs 1514 284 572 64 125 116 53 375 1,589 217 217 1,806 5,649 2,227 1,556 Holly Springs 1515 90 338 73 141 19 8 142 811 7 7 818 4,483 1,531 1,021 Holly Springs 1516 186 351 9 248 329 24 569 1,716 8 8 1,724 7,726 2,850 1,371 Holly Springs 611 1,277 188 602 547 180 1,334 4,739 281 281 5,020 23,328 8,712 6,258 Waleska 1474 22 107 46 30 62 49 316 19 19 335 1,220 454 1,243 2,689 Waleska 1475 309 15 53 138 15 461 991 85 85 1,076 1,640 614 3,119 Waleska 1477 126 33 10 311 169 30 96 775 59 59 834 3,339 1,210 10,855 Waleska 1478 79 17 2 205 143 16 97 559 191 191 750 2,780 1,060 6,125 Waleska 536 172 12 615 480 123 703 2,641 354 354 2,995 8,979 3,338 1,243 22,788 Woodstock 1513 43 4 36 38 26 131 278 23 23 301 1,604 636 906 Woodstock 1529 55 23 657 194 236 239 1,404 5 5 1,409 2,270 931 735 Woodstock 1531 15 53 24 280 175 219 766 48 48 814 6,337 2,701 740 Woodstock 1532 41 2 10 53 52 76 234 16 16 250 3,877 1,491 930 Woodstock 1533 52 21 6 13 286 105 312 795 210 210 1,005 2,435 947 989 Woodstock 1534 107 15 1 412 108 589 1,232 75 75 1,307 2,166 1,000 411 Woodstock 1535 36 1 97 61 226 421 19 19 440 908 393 233 Woodstock 1536 42 6 13 195 183 400 839 50 50 889 4,843 1,810 743 Woodstock 1537 164 848 395 278 368 31 942 3,026 117 117 3,143 2,841 1,264 1,323 Woodstock 1538 57 128 215 58 941 78 1,258 2,735 239 239 2,974 2,154 973 518 Woodstock 1539 59 44 116 79 473 89 597 1,457 53 53 1,510 1,842 799 415 Woodstock 1541 90 10 153 811 22 583 1,669 56 56 1,725 3,122 1,202 870 Woodstock 1545 33 18 95 734 105 1,168 2,153 263 263 2,416 8,814 3,163 2,418 Woodstock 1546 280 2 21 76 455 104 360 1,298 1,156 1,156 2,454 8,440 3,325 1,811 Woodstock 1,074 1,076 852 1,493 5,337 1,375 7,100 18,307 2,330 2,330 20,637 51,653 20,635 13,042 Source: Atlanta Regional Commission. January 21
A TLANTA R EGIONAL C OMMISSION 40 COURTLAND S TREET, NE A TLANTA, GEORGIA 30303 Appendix C: Mobility Forecasts Forecast Study Area The Mobility forecasts are for the13 county area that comprises the Atlanta Air Quality Nonattainment area. It includes the 10 ARC counties (Cherokee, Clayton, Cobb, DeKalb, Douglas, Fayette, Fulton, Gwinnett, Henry and Rockdale), plus Coweta, Forsyth and Paulding. Forecasting Methodology ARC produces longrange forecasts using a twostep method. The first step produces forecasts for the entire 13county study area as a whole. The second step disaggregates the studyarea forecast to census tracts and traffic analysis zones (TAZs). Study Area Forecasts The forecast for the entire 13county study area is produced using a mixed econometric and cohort component model called IPEF (Interactive and Econometric Forecasting). This model divides the population of the region into small groups (cohorts) whose members are of the same race and sex and nearly the same age. Operating in 5year iterations, the model assesses the effects of the three ways population can change, births, deaths and migration, on each cohort. The model uses birth and death rates forecast by the U. S. Bureau of the. Migration is determined as the population movement required to create a labor force sufficient to meet the needs of the econometric forecast of jobs. The econometric module of the model is calibrated against historical employment and population data. Its inputs include an industry specific forecast of national employment and forecasts of future laborforce participation rates. Because population is partly a function of employment and vice versa, the model is iterative. It cycles until the employment and population are in balance. ARC staff produce the studyarea forecasts with the assistance of a team of local experts in economics and demography. This technical advisory committee advises on the calibration of the model and assists in the development of assumptions affecting the forecasts. When complete, the committee recommended the study area forecasts to the Commission. ARC Methodology 22
A TLANTA R EGIONAL C OMMISSION 40 COURTLAND S TREET, NE A TLANTA, GEORGIA 30303 Small Area Forecasts The primary tool used to disaggregate the studyarea forecasts to smaller areas (census tracts in the Atlanta application) is a model called DRAM/EMPAL (Disaggregated Residential Allocation Model/EMPloyment ALlocation model). Calibrated against historical data for the study area, this model attempts to replicate observed growth patterns. Like the IPEF model, it operates in fiveyear cycles. Each successive forecast becomes the base for the next. Inputs for each census tract include baseyear households by income, employment by industry, land use by type and mathematical measures of accessibility to each of the other census tracts in the study area. The accessibility measure is based on anticipated changes in the regional transportation system. ARC staff held extensive meetings with local government planning staffs to determine how local policies would affect population and employment distribution at the smallarea level (designation of a substantial area as greenspace or the ongoing development at Atlantic Station, for example). Where appropriate the findings from these discussions were incorporated into the model. ARC s process for developing local government input to the forecasting process is discussed in detail in Appendix A. The accessibility measures used in the DRAM/EMPAL model are produced using the TP+ travel demand model. TP+ is a mathematical model of the study area s transportation system. Futureyear transportation networks are developed in a complex process that considers regional mobility, regional equity, air quality, and financial constraints on future improvements. TP+ requires input at the traffic analysis zone (TAZ) level. TAZs are subdivisions of census tracts (The 589 census tracts in the forecast study area are divided into 1,683 TAZs.) A relatively simple Zonal Allocation Procedure (ZAP) is used to further disaggregate the DRAM/EMPAL forecast for each censustract to its constituent TAZs. ARC Methodology 23
Appendix D: The Data Regression Process The term regression when used in projecting historical data into the future is a mathematical expression for a method of finding trends in the known data on which the projections can be based. Some refer to this as curvefitting because the process attempts to find the mathematical line 9 that best fits the known data points; continuing this line into the future produces the projection. The best fit line is the line that has the highest correlation to the data that is, the line with data points that are, collectively, the closest to reproducing the historic data points. In some cases, of course, the best fit is not the most realistic projection, as discussed below. Demographic data is highly complex and rarely fits neatly along a simple line. On the other hand, demographic data regarding population and employment most often reflect a progression from the past into the future as change occurs. Some years may show a much greater change than others, but trends in these changes over time are usually evident. Regression analysis, then, attempts to fit a straight line (1 st order regression), a parabolic line (2 nd order, which assumes a steady change that is constantly increasing or decreasing), and an ess curved line (3 rd order, which assumes that the trend is to go up for awhile and then down, or vice versa) to best define the trend in the data. Ultimately, fitting trend lines to historic data must be viewed as an approximation at best, and extending these lines into the future is useful as an analytical tool, an indicator of the future, but not necessarily a prediction of reality. Best Fit Regressions To illustrate the regression analysis process, particularly when the historic data is relatively continuous such as population counts, the Data Table on the right has been created for use as an example. The table shows the historic data that has been created, as well as the 1 st, 2 nd and 3 rd order regressions that have been calculated against the historic data (the straight line, the parabola and the ess curve, respectively). The correlations indicate the fit to the data, with a 1.0 being a perfect fit and 0.0 being no fit at all. First, we ll look at how a regression might treat apparently unrelated, noncontinuous data, in contrast to the example considered here. Then, we ll discuss how well the regressions in the Example Data Table fit the historic data itself to illustrate our example. EXAMPLE DATA TABLE Historic 1970 30,021 22,357 28,976 30,828 1975 31,998 31,200 32,146 30,823 1980 36,524 40,043 37,206 35,354 1985 42,105 48,886 44,158 43,364 1990 51,876 57,729 53,001 53,795 1995 66,520 66,572 63,735 65,588 79,361 75,415 76,361 77,684 88,056 84,258 90,878 89,025 93,102 107,286 98,554 101,945 125,585 105,210 110,788 145,775 107,937 119,631 167,856 105,675 128,474 191,829 97,366 Correlations: 0.9475 0.9908 0.9962 9 In mathematical terms, a line may be straight or curved. A curved line usually traces a mathematical formula, such as a parabola or ess curve function, when used in regression analyses. January 24