ctpp-news December 1998

ctpp-news@mailman.chrispy.net

14 participants
19 discussions

FW: 1999 ESRI Federal User Group Meeting - Call for Presentations

by Todd Rogers

2nd Annual ESRI Federal User Group Meeting Call for Presentations April 29-30, 1999 National Geographic Society, Washington, D.C. YOU MAKE IT HAPPEN! An important component of a user group meeting is the exchange of information among users. Many years of GIS experience are collectively shared and disseminated through presentations for users by other users. The 1999 ESRI Federal User Group Meeting is a unique opportunity for you to meet with other ESRI federal users to discuss important issues and exchange information on how GIS technology can help solve complex problems within your industry. We would like to invite you to share your GIS project or application. If you are interested in giving a presentation or demonstration of your federal GIS project or application, please send us the information listed below via e-mail to dpaxson(a)esri.com <mailto:dpaxson@esri.com> or FAX to 909-307-3074 to Dana Paxson, no later than Friday, February 5, 1999. Name: Organization: Phone: FAX: E-mail: Presentation Description: More details on the meeting will follow in the next month. We look forward to seeing you in Washington, D.C.! Todd Rogers Federal Business Development <mailto:Trogers@esri.com> Trogers(a)esri.com 2070 Chain Bridge Road, Suite 180 Vienna, VA 22182-2536 Tel 703-506-9515 Fax 703-506-9514

25 years, 10 months

Re: [CTPP] CTPP

by phillip_a_salopek＠ccmail.census.gov

Nathan and the CTPP newsgroup: A few comments on Nathan's 12/9/98 posting. First, we hear what you are saying, Nathan, regarding your interest in NYSDOT in getting block group data, over and above what the MPOs receive. We are trying to see how we might accomodate this; we'll keep everyone posted through this newsgroup on the progress. Secondly, however, I have to point out that a number of the assumptions you have regarding the production of the CTPP and its relation to STF3 are just plain wrong. The CTPP is --NOT--repeat NOT-- part of STF3. The CTPP is programmed by a different group of people, at a different time, independently of anything done for STF3. The only thing they have in common is that they both use the same source file, our internal sample edited detail file. We formatted the CTPP to look like STF3 to make it easier for people who were accustomed to using Bureau summary tape files. But the whole idea behind the CTPP is that it is CUSTOM (read non-standard) content for CUSTOM geography. The content is tailored to transportation planning uses and consists of much more detailed cross-tabulations than the single variable distributions found on STF3. Even if the Bureau produced a workplace-based STF3 as you suggest (an idea which has been rejected in the past), my understanding is that the content would still be lacking for transportation planning uses. So while this is a legitimate issue for people interested in place of work data generally, it's not really a CTPP issue. On the other hand, although we make the CTPP content available for standard Census geographic units like tracts or block groups, most MPOs choose to have the data created for TAZs, a non-standard or custom geographic unit. So even if the content of STF3 was more detailed (which for 2000, it will not be) the geography wouldn't be as useful for transportation planners and there would still be a need for a CTPP. So it seems to me that there's really little point in talking about STF3 in relation to CTPP. They aren't related. Similarly, there is no standard census product that provides county-to-county work flows. The file produced in December of 1992 that Chuck mentioned (STF-S-5) was again a special tabulation done out of this office for a number of customers, one of which was BEA whom I believe produces the REIS CD you mentioned. (In other words, if we don't produce the special tab, there is no data for them to put on their CD.) This product lacks the means of transportation, travel time, and peak/off peak information provided in CTPP Parts 3 and C, which I assume transportation planners generally find to be valuable. This product was produced by the CTPP programmers (again having nothing to do with STF3) and would have been done considerably later, IF AT ALL, had it relied on non-CTPP staff. Yes, it probably delayed the first releases of CTPP by a few months, but as Chuck indicated, it was a product that was used by the transportation planning community as well as others like BEA, BLS, etc. For 2000, I assume that as in the past, there will not be a county commuter flow product created as a standard product. If sponsors are found for such a product, then the likelihood that it will be created is increased. My own opinion is that if such a tabulation is going to be produced, we should try to broaden its scope and include characteristics of the commuters between counties, not just counts. I think this would make the product more marketable to a larger audience. However, it would also likely increase the size and complexity of the dataset. We might also consider producing commuting flows for lower-level geography (say, places above a certain size), as part of such a product, but I haven't really seen the demand for this. I'd be inclined to say that what we do in the statewide CTPP for place-level flows is sufficient. You also mention that Census geographic units should always be available as a summary level. Well, this is your opinion and you're entitled to it, BUT, I think it's a rather narrow view. First, I think the evidence indicates that this is a minority view in the transportation planning community. In 1980 we produced something called Part V of the UTPP which was data by block group of work, even where the rest of the package was tabulated for TAZs. I know of very few people who used these data. In 1990 we did something similar, producing Part 7 of the CTPP in all urban packages which was data by tract of work. Use of Part 7 has been isolated at best. So it is clear to me that TAZs are of primary importance and there is little demand for standard census geography summaries as you suggest. I have comments on some of the other points you made, but this is too long already, so I'll end here. But I encourage you and others to continue to voice your sentiments and concerns. We may not always agree, nor be able to implement your suggestions, but we will listen and try to make improvements. --Phil

25 years, 10 months

Archived Posts

by ed c

an archive version of the ctpp news is now available at http://www.chrispy.net/ctpp-news/ it is not glamorous but it does the job. for those like me that do not store book marks very well, you can find the link on our web site on the page that talks about the mail list. here is the direct link to that page http://www.mcs.com/~berwyned/census/maillist.html

25 years, 10 months

NEWS ALERT

by ed c

Date: Mon, 14 Dec 1998 From: Census2000 <Census2000(a)ccmc.org> House Leaders Consider Shifting Census Oversight to Internal Watchdog Committee Monitoring Board, House Panel Continue Hearings House Republican leaders are considering a proposal to transfer jurisdiction over the census to the House Oversight Committee, which is responsible for congressional office budgets, campaign finance reform and contested elections, and operations of the House generally. The pending change was reported last week by the Capitol Hill newspaper Roll Call and confirmed by lawmakers and staff aides who work on census issues. Under the proposal, the Subcommittee on the Census of the Government Reform and Oversight Committee, created a year ago, would be eliminated. Rep. Carolyn Maloney (D-NY), the senior Democrat on the census subcommittee, strongly criticized the proposed shift. "The Leadership felt their control on this issue slipping away. People are becoming more aware of their ploy to be sure America's minorities remain anonymous," Rep. Maloney said in a written statement. She accused Republican leaders of "burying the Census issue in a paper pushing committee." Census Subcommittee Chairman Dan Miller (R-FL) has not yet issued a statement. He and Rep. Maloney were presiding over a hearing in Miami, FL, last Thursday to examine local efforts in support of the census. The House Oversight Committee has six Republican and three Democratic members; the Government Reform panel's current party ratio is 24 to 19, plus one Independent. Chaired by Rep. William M. Thomas (R-CA), the Oversight panel has no subcommittees. The committee's senior Democrat in the 105th Congress, Rep. Sam Gejdenson (D-CT), is leaving the panel. Roll Call also reports that Republican leaders might change the panel's name back to the Committee on House Administration, the title used when Democrats were in the majority. Responsibility for overseeing Census Bureau activities in the House of Representatives has shifted several times in recent years. Prior to 1995, the Subcommittee on Census and Population (later called the Subcommittee on Census, Statistics, and Postal Personnel) of the Committee on Post Office and Civil Service had jurisdiction over the Census Bureau and broader issues related to the Federal statistical system. The entire committee was eliminated when Republicans assumed the majority in 1995, and jurisdiction over the census was handed to the Subcommittee on National Security, International Affairs, and Criminal Justice of a revamped Government Reform panel. The national security subcommittee was chaired by former-Rep. William Zeliff (R-NH) in the 104th Congress, and then by Rep. J. Dennis Hastert (R-IL) for the first year of the 105th Congress. Republican leaders created the new census subcommittee at the start of 1998 and named Rep. Miller as chairman. It is unclear whether the House Oversight Committee would monitor all Census Bureau activities and other data issues or just the 2000 census. Another subcommittee under the Government Reform panel has been examining changes to the Federal rules governing the collection of racial and ethnic data. Monitoring Board continues hearings: The Census Monitoring Board will hold a hearing in Sacramento, CA, on December 16, to discuss the nearly-completed census dress rehearsal. Sacramento was one of three sites where the Census Bureau conducted a dry-run of census operations this year. Under a congressional directive to prepare for two census designs, the Bureau carried out its original plan in Sacramento, which included sampling to complete follow-up visits to unresponsive households and a post-census quality check survey to measure and correct under-and overcounts. The Board's hearing will take place from 8:00 a.m. - 12:30 p.m., in the City of Sacramento Council Chambers, 915 "I" Street. The meeting is open to the public. Congressional hearings continue: The House Subcommittee on the Census held a hearing in Miami, FL, last Thursday to discuss ideas from local officials and community organizations on how to ensure an accurate census. According to a December 11 article in The Miami Herald, witnesses from community-based organizations and Rep. Carrie Meek (D-FL) told the lawmakers that statistical methods must be used in addition to the traditional mail and door-to-door counting. Rep. Maloney praised a letter in support of the Census Bureau's 2000 plan signed by nearly two-dozen local groups including the Urban League, the Alliance for Aging, the Haitian American Foundation, and the Miami-Dade County Hispanic Advisory Board. Chairman Miller said that more aggressive promotion could improve the accuracy of the census and noted that two Federal district courts concluded this summer that sampling was unlawful. At a press conference earlier in the week, Miami-Dade County Mayor Alex Penelas announced the formation of a Complete Count Committee to oversee and coordinate local activities in support of the 2000 census. Mayor Penelas said the area's net undercount of 70,000 in 1990 "shortchanged" the community. "For a successful Census that includes everyone, we need to use statistical techniques such as sampling," he noted. The Mayor was joined by representatives of community organizations including the NAACP, American Association of University Women, Organization of Chinese Americans, and Cuban American National Council, Inc. All of the groups stressed the importance of census participation in their communities and voiced support for the use of sampling to supplement the direct counting effort. The subcommittee plans additional field hearings to discuss ideas from local officials and community-based organizations on improving the census process. At the December 3 - 4 meeting of the 2000 Census Advisory Committee, Chairman Miller's staff announced sessions in Phoenix, AZ, on January 28, and Los Angeles, CA, several days later. The hearings were disclosed before word of the subcommittee's possible elimination became public. Congressional committee assignments: Republican and Democratic lawmakers continued to make committee assignments in anticipation of the start of the 106th Congress on January 6. Three new Senators will join the Committee on Governmental Affairs, which oversees the census: Sen. Judd Gregg (R-NH), who also chairs the appropriations subcommittee responsible for the Census Bureau's budget, and freshmen Senators George Voinovich (R-OH) and John Edwards (D-NC). The new committee members will replace Senators Sam Brownback (R-KS) and Don Nickles (R-OK) and retiring Sen. John Glenn (D-OH), the panel's senior Democrat. The Census 2000 Initiative will publish a roster of all congressional committees with responsibility for census funding and oversight after the 106th Congress convenes and panel assignments are complete. Questions about the information contained in this News Alert may be directed to TerriAnn Lowenthal at (202) 484-2270 or, by e-mail at <terriann2k(a)aol.com>. Please direct all requests to receive News Alerts, and all changes in address/phone/fax/e-mail, to Census 2000 at <Census2000(a)ccmc.org> or 202/326-8700. Please feel free to circulate this information to colleagues and other interested individuals.

25 years, 10 months

testing...

by Chris Parrinello

testing a new majordomo configuration. Please ignore this message. Sorry for the inconvenience. Thanks, Chris

25 years, 10 months

Table Content -Reply

by Nathan Erlbaum

if you have ever looked at the table headings they are sometimes very difficult to figure out what they actually contain. For instance, if you want the JTW number of workers by mode there really isn't a table heading for this. JTW is part C and table C1 is time to work. Its heading is "Time leaving home to go to work-total and peak period by means of transportation to work"...universe workers 16+ who did not work at home. Each cell contains the number of workers, not the time they spent going to work by that mode; the table coordinates tell you that the table contains 2 tables sequentially first coordinates 1,1 to 1,19 contain the total and then the peak period with table coordinates 2,1 to 2,19. Table headings should be immediately intuitive!!!!! What needs to be done is that the table headings for C1 must say what the table contains:" workers, leaving home to work by mode of travel; daily and peak period" universe of workers 16+ who did not work at home. This way you immediately know the contents are workers all day and peak period Get an English teacher to write or review the headings, the products produced by Census are written in Census Jargon which at best is unclear because it tries to be overly precise and interpretation can be very tough even knowing what you are reading. >>> ed c <berwyned(a)mcs.com> 12/10/98 06:20pm >>> below is a dialogue that has been going on that i believe would be of interest to the entire ctpp mail list. it is extremely topical because just today Elaine Murakami called to remind me that i need to get something written up regarding our survey of several trb committees regarding the content (tables) of the ctpp package. here is a web page that presents some preliminary work in that area. don did remind me of an early product that even we in chicago used (stf s-5). http://www.mcs.com/~berwyned/census/notes/content.html needless to say any comments folks have on content for the ctpp (the tables) would be appreciated. i also recommend that you post your comments to the list ed christopher ------------------------------------------------ Don, Let me see what I can answer right now and what has to go into the hopper: > Place of work outside SMSA of residence. This needs a further > breakdown. Our Cincinnati area is a 13 co. CMSA so the data for > "outside each pmsa" doesn't tell me if the worker is in the other > pmsa. Similarly, we are adjacent to the Dayton msa and I can't > tell if the workers are coming to or from there. The county and > major city breakouts in this table are also valuable. (CBD?) > These concerns apply mainly to the standard tabulations. I > strongly recommend that the STF-S-5 commuter tabulations > be prepared again for nation-wide county to county work > trip commuting. I actually depend on > these for my regional in and out commuting and, consequently, > the regional net employment. I think the work flows have to come from the county to county file, and I would assume that will be repeated. It will make sure it's on our list. Actually, I was never aware of it as a formally named product (STF5?) but I did have a copy of it for Michigan counties. The issue of grouping counties as areas on the CTPP has to be fought out within the transportation planning community. > Another issue is continuation of the non-motorized travel modes > of biking and walking along with working at home. (Assuming > that transit and carpool modes will be continued.) These are > becoming more important in our region as we deal with air > quality conformity, congestion reduction and sprawl. Bicycle, Walked, and Worked at home are on the census dress rehearsal questionnaire, which means that unless something very unusual and unlikely happens, they will be on the 2000 long form. Once the data are collected, it's really up to the transportation planning community to decide how they will be tabulated on the CTPP. Also, you are going to have more opportunity to do your own tabulations via the Internet, so if you need something special you will probably be able to do it (albeit for a fee), or pay someone to do it for you. > Finally, an issue that I am assuming will be fixed with the > 2000 CTPP is place of work coverage in the suburban > and rural areas of our metro area. In 1990, less than half > of a county's workers were 'assigned' to a TAZ of work > in three of the 8 counties in our MSA. With nationwide TIGER coverage, I believe that all workplaces with street addresses are to be coded to tract/block. This of course permits their assignment to TAZ. The question is what happens with the inadequate workplace address entries on the census. You might want to talk to Phil Salopek about their plans on this. In 1980 Phil Fulton devised an elaborate allocation algorithm which fixed a lot of the problems in these data for workplaces inside the urbanized area, and with the full TIGER coverage the algorithm can be run for everywhere. However, if you have some major workplaces in the more rural counties that don't have addresses and that you want to be sure are coded correctly, you may be able to provide some workplace name information to the Bureau to assist with this. > And that brings to mind another final issue. In 1990, our CMSA > and MPO included the same 8 counties. In 1993, five more > counties were added to the CMSA, but not to our MPO > planning area. Therefore, our 2000 CTPP > will not include the added CMSA counties. Does this matter? The CMSA and the MPO don't have anything to do with each other, really. The CMSA is defined under OMB rules (now under review for possible significant changes; a federal register notice is due very soon); there can be a considerable amount of politics in the MSA/PMSA/CMSA designations because a lot of people think "the bigger the better" which makes for larger CMSAs. If you're not planning for the additional 5 counties, you probably don't need the CTPP for them. Besides, won't some other MPO have it (if the 5 counties are their own PMSA, they probably have some MPO coverage somewhere). > Thanks for asking! Hope this helps! > (copied to Ed Christopher) Ed, if you want to post this to the list, please feel free. ============================= Patricia C. (Patty) Becker 313/535-2077 APB Associates/SEMCC FAX 313/535-3556 17321 Telegraph #204 Home 248/355-2428 Detroit, MI 48219 pbecker(a)umich.edu

25 years, 11 months

Table Content

by ed c

below is a dialogue that has been going on that i believe would be of interest to the entire ctpp mail list. it is extremely topical because just today Elaine Murakami called to remind me that i need to get something written up regarding our survey of several trb committees regarding the content (tables) of the ctpp package. here is a web page that presents some preliminary work in that area. don did remind me of an early product that even we in chicago used (stf s-5). http://www.mcs.com/~berwyned/census/notes/content.html needless to say any comments folks have on content for the ctpp (the tables) would be appreciated. i also recommend that you post your comments to the list ed christopher ------------------------------------------------ Don, Let me see what I can answer right now and what has to go into the hopper: > Place of work outside SMSA of residence. This needs a further > breakdown. Our Cincinnati area is a 13 co. CMSA so the data for > "outside each pmsa" doesn't tell me if the worker is in the other > pmsa. Similarly, we are adjacent to the Dayton msa and I can't > tell if the workers are coming to or from there. The county and > major city breakouts in this table are also valuable. (CBD?) > These concerns apply mainly to the standard tabulations. I > strongly recommend that the STF-S-5 commuter tabulations > be prepared again for nation-wide county to county work > trip commuting. I actually depend on > these for my regional in and out commuting and, consequently, > the regional net employment. I think the work flows have to come from the county to county file, and I would assume that will be repeated. It will make sure it's on our list. Actually, I was never aware of it as a formally named product (STF5?) but I did have a copy of it for Michigan counties. The issue of grouping counties as areas on the CTPP has to be fought out within the transportation planning community. > Another issue is continuation of the non-motorized travel modes > of biking and walking along with working at home. (Assuming > that transit and carpool modes will be continued.) These are > becoming more important in our region as we deal with air > quality conformity, congestion reduction and sprawl. Bicycle, Walked, and Worked at home are on the census dress rehearsal questionnaire, which means that unless something very unusual and unlikely happens, they will be on the 2000 long form. Once the data are collected, it's really up to the transportation planning community to decide how they will be tabulated on the CTPP. Also, you are going to have more opportunity to do your own tabulations via the Internet, so if you need something special you will probably be able to do it (albeit for a fee), or pay someone to do it for you. > Finally, an issue that I am assuming will be fixed with the > 2000 CTPP is place of work coverage in the suburban > and rural areas of our metro area. In 1990, less than half > of a county's workers were 'assigned' to a TAZ of work > in three of the 8 counties in our MSA. With nationwide TIGER coverage, I believe that all workplaces with street addresses are to be coded to tract/block. This of course permits their assignment to TAZ. The question is what happens with the inadequate workplace address entries on the census. You might want to talk to Phil Salopek about their plans on this. In 1980 Phil Fulton devised an elaborate allocation algorithm which fixed a lot of the problems in these data for workplaces inside the urbanized area, and with the full TIGER coverage the algorithm can be run for everywhere. However, if you have some major workplaces in the more rural counties that don't have addresses and that you want to be sure are coded correctly, you may be able to provide some workplace name information to the Bureau to assist with this. > And that brings to mind another final issue. In 1990, our CMSA > and MPO included the same 8 counties. In 1993, five more > counties were added to the CMSA, but not to our MPO > planning area. Therefore, our 2000 CTPP > will not include the added CMSA counties. Does this matter? The CMSA and the MPO don't have anything to do with each other, really. The CMSA is defined under OMB rules (now under review for possible significant changes; a federal register notice is due very soon); there can be a considerable amount of politics in the MSA/PMSA/CMSA designations because a lot of people think "the bigger the better" which makes for larger CMSAs. If you're not planning for the additional 5 counties, you probably don't need the CTPP for them. Besides, won't some other MPO have it (if the 5 counties are their own PMSA, they probably have some MPO coverage somewhere). > Thanks for asking! Hope this helps! > (copied to Ed Christopher) Ed, if you want to post this to the list, please feel free. ============================= Patricia C. (Patty) Becker 313/535-2077 APB Associates/SEMCC FAX 313/535-3556 17321 Telegraph #204 Home 248/355-2428 Detroit, MI 48219 pbecker(a)umich.edu

25 years, 11 months

Mailing list

by Frey-DPW, Bob

Greetings Ed Christopher: Please place me on the CTPP e-mail list server so I can contribute to it and view others correspondence. Thanks, Bob Frey Massachusetts Highway Department bob.frey(a)state.ma.us

25 years, 11 months

CTPP

by Nathan Erlbaum

At Ed Christopher's suggestion I am posting this to the list server. The following are some observations on the E-mail traffic I have been observing with respect to the CTPP summarization issues that I have raised with Ed at and since his sub-committee meeting at TRB last January. I must note that more recent e-mail is now starting to mention non-TAZ needs Phil Salopek in a recent e-mail says if you want Census geography instead of TAZ you don't have to participate in the TAZ up program....well at NYSDOT we want the statewide element of the CTPP to be detailed to CDP or lower and all the urban area elements for our use to be detailed to Census geography....tract and block group as the lowest level in the urban area. NYSDOT is interested in Census geography at the block group level especially in urban areas. Since each of the MPOs will be responding separately to the CTPP TAZ questionnaire, in addition to NYSDOT, then MPOs will indicate their need for TAZs or census geography. This way the MPOs can get what they want and the state can get what it needs. The glitch is if Census or Phil Salopek says the state has to have it the MPO way. Frankly I don't see the problem....the CTPP is part of the STF3. As part of STF3 it is summarized for CTPP parts A and 1 to the block / block group level and everything above from the get go. All that is required is the production of STF3 for the work place. County work flow is produced very early on in Census processing prior to the CTPP. These data are historically available on the REIS CD. So for the most part Census provides CTPP part C or 3 at the county level outside of CTPP. Clearly they have the routines in place to do it by specifying lower geography with selected focus (such as state or metro area). So its not just a CTPP processing software issue. The real issue is getting Census to recognize several things: 1 Census geography should always be available as a summarization level for all locations 2 If you are not an urbanized area 50,000+ then you likely do not have an MPO, and you do not have TAZs even though you may be a small urban area 3 TAZs are unique to "MPOs with models" and they don't define TAZs them the same way 4 If you are not now an urban area now and eventually become one in say 2002 then you are out of luck if TAZ is the only summarization level. This may be especially painful when we move to the ACS. 5 If you need to add TAZs , combine or subdivide them later you can't 6 This is not just an MPO product 7 This is really a summarization level issue like congressional boundaries 8 The problem that Census really needs to address is how to aggregate data up from lower geography for values such as mean and median; where summarization is really not possible ( median income or median travel time for example). Resolving this problem then enables Census or the end user to create the data at the lowest possible geographic unit and provide a summary level routine for computational values. All the MPOs need then is a simple lookup table to relate TAZs to Census geography and a routine to fix the computational values 9 From a purely economic product perspective Census geography means you can sell the product to third parties and recover the cost. TAZ is a summarization level unique to MPOs. There are lots of value added resellers of STF3 data now in addition to Census. The CTPP creates the workplace version of STF3 for a number of measures that are important to not only transportation planners but also to anyone interested in who, how and/or what arrives at work place locations. 10 Remember to make sure that the CTPP coding uses Census FIPS codes and not Census Place codes that Caliper used in 1990, otherwise it will not directly match common tiger based coverages. 11 The CTPP software that extracts the data table components from the CD rom needs to be improved on the data extraction part. Often one wants some range of Fips or town county, state codes for either the residence , work place or JTW and for selected fields (e.g. total trips, transit). As the 1990 CTPP software works you get all geography that you can point to on the map, not bad on the statewide side except if you want trips from selected origins outside the state. If you are using the urban element then selection is much more difficult because of the level of detail. In either case JTW from selected to selected geography is not easily do-able except in a database product. Some accommodation on the direct data selection side rather than through the visual graphical user interface would be helpful. Something like "extract" the Census routine for use with the Census STF CDs would be helpful. Otherwise you really need a database product like SAS, Paradox, dBASE or Access to get at the data the way you want. 12 What would really help would be Census creating STF3 for the workplace and the present county work flow data for lower summarization levels 13 Lastly it might be useful to note that at NYSDOT many of the information requests I receive come from the economic development interests. These requests reflect transportation or government concerns for attracting businesses into NYS. They come from within our agency or from our State Economic Development agency. These questions typically ask about workers first and then where they live. NYS can't be that different from the rest of the states that compete for the location of new jobs. Many of these requests are for areas just outside of the urban boundary. The fact that these type of informational questions are being asked illustrates the value of detailed Census geography and summarization levels beyond what has been provided for at the metropolitan planning through TAZs. As always I am available to discuss some of the more mechanical technical aspects of using the CTPP data in non TAZ analyses with anyone who wants to discuss why one size does not fit all.

25 years, 11 months

Development of TAZs for the 2000 CTPP (From Thabet Zakaria)

by Margaret Shaw

The following message is from Thabet Zakaria <DVRPC>, not from Margaret Shaw. Please direct all correspondence regarding this mailing to Mr. Zakaria, NOT to Ms. Shaw. Mr. Zakaria's e-mail address is: tzakaria(a)dvrpc.org Thank you. Development of TAZs for the 2000 CTPP This is a brief description of the Traffic Analysis Zones (TAZ) in the Delaware Valley Region, which includes an area of 3,833 square miles and a population of about 5.2 million. I have prepared this summary in the hope that other areas in the country will find it useful for preparing a zonal system for the 2000 CTPP. In 1960, the Penn Jersey Transportation Study developed a set of TAZs for data collection and travel simulation within the cordon area (urbanized area) which did not consider county boundaries. The basic unit was a modified grid square, 0.10 mile on a side in city centers and 0.50-mile elsewhere. A total of 162 districts (TAZs) were aggregated to 51 Superdistricts for evaluation and presentation. In the late 1970s, DVRPC realized that it could not continue to collect massive data for transportation planning, and must depend on secondary sources, including the Bureau of the Census. It was decided to adopt census geography and convert the old TAZs to census tracts and block groups. Census tracts were considered adequate for regional travel simulation, except for the Philadelphia CBD, where block groups were used to define TAZs. The cordoned area was expanded to the region's county boundary and divided into 1,330 TAZs, which were aggregated to 71 county planning areas to simplify analysis and presentation. This system of TAZs was expanded in the 1980s, because the Bureau of the Census in cooperation with the counties divided some census tracts for the 1990 Census. This system proved to be easier to work with and facilitated the preparation of a correspondence table for the 1990 CTPP between TAZs and blocks. It should be noted that the new TAZ system is not free of problems. Some tracts are too large or too small for network coding and modeling, and they must be reviewed each decade because of tract splitting. Also, some tracts are too narrow or curvilinear, and are thus not suitable for travel simulation purposes. It is essential that each tract in the area be examined regarding its layout, size, type and magnitude of development. Several criteria could be used to develop TAZs form census geography, such as population, employment, trip production, trip attraction, zone centroid location, and trip loading (network grain). DVRPC used an average of about 4,000 persons and 3,000 employees per zone in the development of its TAZ system. Obviously, the size of TAZs should be smaller for corridor and sub-area studies and small MPOs.

25 years, 11 months

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ctpp-news December 1998