Q1: Where do I get TIGER data and detailed information about the data set? The most recent version is the 108th Congressional District TIGER/LineŽ Files, and are available on-line. Earlier versions of TIGER/Line data are available on CD-ROM from the Customer Service Center at 301-763-4636. If you are only interested in one or two states you could buy just one CD ($60) since several states are grouped on a CD. Note that the 1998 version of this product are the data used in the TIGER Map Service (a custom application). The TIGER/Line files do not come with viewing software. To use the data you must have a Geographic Information System (GIS) package, mapping software or write your own software that can import TIGER/Line files. The technical documentation provides detailed information for the current TIGER/Line (108th Congressional District TIGER/Line, 2002 TIGER/Line, UA TIGER/Line and earlier versions) data sets. These files may be downloaded from our Web site. The Census TIGER page address is: http://www.census.gov/geo/www/tiger/ _________________________ Q2: Where did the data come from that is used in the TIGER Map Service? The source for the map base in the TIGER Map Service (TMS) is our TIGER data base which we developed to automate the mapping we need to do for the census. A by product of that data base is a product called TIGER/Line. We use a version of it in the TMS as well as sell it for outside use. Many of those PC-based street mapping packages one sees in the stores are based on it. The source materials used in developing the TIGER data base are principally the following: 1:100,000 US Geological Survey (USGS) topographic maps that were scanned by USGS for the Census Bureau. The USGS scanned the roads, railroads, hydrographic features, and miscellaneous transportation features layers. These layers were then vertically integrated by us into a topologically consistent file (not stored as separate layers). For the 2% of the land area covered by the major urban areas we substituted the GBF/DIME files that we had created in the '70s (with updates in 1981 to 1985). The resulting TIGER data base file was in turn updated by maps obtained from local officials and some field work done by Bureau staff. The Bureau also tagged all the features with the geographic codes needed to identify the areas for which it collects and tabulates data (essentially all administrative and statistical area boundaries). You can visit our TIGER page for more information: http://www.census.gov/geo/www/tiger/ Of the products you'll see listed, the closest to TMS (a map display package) is LandView 5. The TIGER/Line product are just the data (in ASCII format) without any display software. You can download data sets for the 108th Congressional District TIGER/Line, 2002 TIGER/Line and the UA Census 2000 TIGER/Line files which supercede the Redistricting Census 2000 TIGER/Line files. You can also download a LandView 5 sample software and data set. Contact the Customer Service Center at 301-763-4636 for ordering information. __________________________ Q3: Does TIGER/Line or the TIGER Map Service have topographic (terrain) data? The TIGER data does not include topography. This information wasn't needed for Census Bureau operations. While it might be classed as "nice to have", the cost of integrating it into TIGER would have been be high. TIGER is not structured in layers as one might see in a typical Geographic Information System data base. Therefore one could not simply add a layer of topography to the data set. Note, you may see the terms "topology" and "topological" used in reference to TIGER data. These have nothing to do with terrain but are mathematical terms relating, in this case, to a particular approach to data base design. If you're looking for the availability of digital topographic data you might try searching the US Geological Survey Web site for information on Digital Elevation Models (DEMs). http://info.er.usgs.gov/ Another possibility is surfing the Web for geography/mapping sites. ___________________________ Q4: Why are some streets missing from the TIGER/Line products and the TIGER Map Service? Although we tried to include every street, road, most water features, assorted types of boundaries, and other features in the U.S., we know we missed some in the original development operation for the 1990 Census. Census 2000 funding allowed us to do a more comprehensive update, but we probably don't have all of the new features that came into existence after 1990. The Census Bureau is in the initial stages of a multi-year project to update the features in the Census TIGER database and correct their positional accuracy. We expect the 2004 TIGER/Line files to be the first version to reflect substantial updates from this project. For more information about the MAF/TIGER Modernization Project go to URL: http://www.census.gov/geo/mod/maftiger.html ___________________________ Q5: Does TIGER/Line have telephone exchange data or LATA zones? TIGER/Line doesn't contain any data on telephone exchanges or LATA (local access transport area) zones. We won't be adding this type of data since it isn't needed for the applications for which TIGER was designed - cartographic support of the census and other statistical activities of the Census Bureau. While such data might be useful, we are very constrained in what we can spend money for in TIGER improvements. ___________________________ Q6: How accurate are the LandView EPA data? Much of the data in LandView is self-reported by regulated facilities; because EPA does not regulate on the basis of latitude or longitude, such reporting errors may not have been corrected. Users trying to correlate census tract data to specific waste sites should be cautioned to double check the accuracy of each location before publishing their analyses. According to the EPA, some of the addresses in the various EPA databases were coded to ZIP code centroids if they could not satisfactorily geocode the address. One can usually tell such situations since several sites appear to be stacking up over a point. _________________________ Q7: Can I use the LandView CD-ROMs/DVD on a network? To run LandView 5 on a network, the program files must be installed on each user's hard drive. The data and maps are normally accessed from the CD or DVD. You may, however, copy the data and map files to either a local hard drive, or to a network file server, so that many users can simultaneously access these files. A more detailed explanation can be found at: http://www.census.gov/geo/landview/lv5/network_dvd.html ________________________ Q8: What map projection does LandView use? LandView doesn't use a map projection when displaying the map. It is treating the latitude and longitude as rectangular coordinates. The principal use of the software is for large scale mapping of small areas so not using a projection does not significantly affect the accuracy of the maps displayed. _______________________ Q9: How do I find the Census 2000 Tract code for a specific street address? The Census Bureau produced a product specifically to assist institutions comply with the Home Mortgage Disclosure Act (HMDA). It was called the "TIGER/Census Tract Street Index" and was based on 1990 Census geography. There are no plans for a TIGER/Census Tract Street Index (CTSI) 2000 release because many CTSI users have other resources available to them for determining Census 2000 census tracts such as the American FactFinder mapping system and the Census 2000 tract outline maps. For information on Census Tract resources, refer to the Census Bureau's "Guide to Census Tract Resources" page at: http://www.census.gov/geo/www/tractez.html ___________________________ Q10: Are census tract and block numbering area maps available on-line? Currently 1990 Census tract/block numbering area and Census 2000 tract maps are available on-line at the Census Bureau's American FactFinder web site, our newest data dissemination and mapping system. You will find the American FactFinder at URL: http://factfinder.census.gov/ There are Census 2000 Census Tract Outline maps and Census 2000 Block maps in PDF at: http://www.census.gov/geo/www/maps/CP_MapProducts.htm However, if you want an electronic map showing Census 2000 tract boundaries, that you can access from your desktop, take a look at the LandView 5 software and download the Demo file located at: http://landview.census.gov/geo/landview/lv5/lv5.html __________________________ Q11: Are the TIGER(R) data or maps made from the TIGER Map Server copyrighted? Do I need permission to use these resources? No, the TIGER data and the maps made from the TIGER Map Server are not copyrighted. This includes all of the geographic products and maps that the Census Bureau sells or distributes. You do not need our permission to use the data (or maps) in a product or publication. The data used comes from the Census Bureau, an agency of the U.S. Government, and is in the public domain. In fact, many of our products are resold or redistributed by others. Vendors take the basic product, add value to it (snazzier interface, more data, etc.) and resell it. Sometimes they just resell exact copies of the data. That's all perfectly legal and we are happy to see the data redistributed and get wider usage. Many of the PC street mapping packages that have come out in the last few years attest to that. We do, however, have trademarks on a number of our TIGER-related product names. The purpose of trademarking these terms is so customers buying products with those names can be confident in identifying the origin (the Census Bureau in this case) of the products (data) being sold. That shouldn't dissuade anyone from creating products using the TIGER/Line(R) data and TMS maps or even citing our original products as the source of all or part of their product. Hundreds of companies and individuals have done so since the advent of TIGER/Line. Basically it means that you can't name your product with one of our trademarked terms, i.e., either calling your product "TIGER" or "TIGER/Line", or use a Census Bureau trademark within the name of the product or service. However you can say that your product is based on the Census TIGER/Line files. We would prefer that you refer to the Census trademark in describing the Bureau's component of your product or service. The above discussion is not intended to be a legal brief on trademark law but just a quick summary of the general trademark issues relating to our products. _________________________ Q12: Does the Census Bureau produce maps of river networks or other physical features? The Census Bureau doesn't produce maps focusing on physical geography such as river systems. However, we do produce a digital cartographic data file (TIGER/Line files) which does contain hydrography extracted from 1:100k USGS topo sheets for the rural areas and our DIME files for urban areas, with the proper software (Geographic information System), you could extract that information. Note that we didn't design our data base with hydrographic mapping in mind so the data may not be complete enough to meet all your needs. For more info on it you can visit our TIGER page: http://www.census.gov/geo/www/tiger/ A better source of such maps is USGS: 1-888-ASK-USGS. Or try their Web site: http://www.usgs.gov/ Another possibility is the state government. Check to see if they have agencies that deal with the environment, fish & wildlife, etc. They often produce such maps. _______________________ Q13: Where do I get a map of my county? The answer depends on the type of map are you looking for (paper or electronic) and how are you planning to use it. If you want something to use as a graphic image for a Web page you could use the TIGER Map Service (TMS) or American FactFinder to create one on the screen and then download it as a GIF file as mentioned on the TMS page. You can use these images without charge since they are in the public domain. This may not provide you with the detail you want. In that case you would have to import the GIF into a graphics program (like Paintbrush, Corel Draw, etc.) and edit it. The Census Bureau doesn't produce general purpose county maps. For a paper map you should try one of the commercial map companies. Another source of county maps in some states is the state's Department of Transportation. For a local (more or less) set of contacts that might be able to help you find the map you need go to the listing at our Web site of state agencies in our State Data Center Program: http://www.census.gov/sdc/www/ Try using one of the on-line search engines like Google or Yahoo. ___________________________ Q14: What other gazetteer-like resources for cities, towns, and places are available on the Internet? Another data base which lists cities, etc. is the Geographic Names Information System at the US Geological Survey (USGS). This is a data base with all the place and feature names from their maps. The URL for their on-line lookup is: http://geonames.usgs.gov/pls/gnis/web_query.gnis_web_query_form In addition to the latitude and longitude (based on where the name appears on the map, not the center of the feature) they also list other information such as the name of the USGS map sheet on which it appears. By the way, when looking up a populated place in their system enter "ppl" for the feature type. They also sell the data on CD-ROM. ___________________________ Q15: Why don't the 2000 or 1990 vintage Gazetteer Place files include county FIPS codes? The 2000 and 1990 vintage Gazetteer Place files do not include county codes because places do not always nest within counties and are therefore coded on the state level. We do have a product, 1990 TIGER/Geographic Identification Code Scheme (GICS), that gives the county code for places, or parts of places (this is for 1990 geography; a Census 2000 TIGER GICS has not been created.) For more information, visit our online catalog: http://www.census.gov/mp/www/rom/msrom12d.html ___________________________ Q16: Does the ZIP Code file you have available for downloading contain a complete and up-to-date list of ZIP Codes? The ZIP file doesn't include all ZIP Codes because it was based only on those areas for which we had city-style addresses (which leaves out a lot of rural areas). The file was created as a byproduct of another operation (a data product based on the ZIP codes we collected with the 1990 Census data). For this Census data product, we took advantage of the fact that we had some ZIP Code data as a consequence of trying to collect addresses for the Census questionnaire mailout so we published data for those ZIP Codes. This ZIP internal point file is basically the lat/long for the ZIP Codes in that product. We put it on the Web in case anyone found it useful. It was not intended to be an authoritative source on ZIP Codes. Note that the task of creating a lat/long or polygon file of all ZIP Codes is not as easy as it seems since ZIP Codes are not designed to be polygons and can't easily be forced into them - particularly in rural areas. To our knowledge there are no official internal point or polygon files available. However, because of the demand for ZIP Code data and maps, the Census Bureau, for Census 2000, created a new statistical area called the ZIP Code Tabulation Area (ZCTA). ZCTAs are close area approximations of U.S. Postal Service ZIP Codes and were designed to overcome the difficulties of defining clear boundaries to which data could be attached. For more information on ZCTAs go to: http://www.census.gov/geo/ZCTA/zcta.html For more information on ZIP Codes the U.S. Postal Service site may be of interest: http://www.usps.gov _________________________ Q17: Does the Census Bureau produce ZIP Code maps? The Census Bureau doesn't have a mandate to do ZIP code mapping so we don't claim that any ZIP product we have is definitive or complete. In any case we don't produce ZIP code maps. There are several commercial mapping firms that produce ZIP Code maps for selected areas, thought not necessarily agreeing with USPS delineations. A Web search should turn up the names of companies that offer these maps. To our knowledge no one, not even the USPS, has produced a complete and authoritative ZIP Code map of the entire country. Another possible source of information is the Postal Service Web site: http://www.usps.gov/ We have produced, as a by product of other work, a point file containing a calculated internal point. This point was calculated in the computer from the locations of addresses with a specific ZIP Code and not out in the field using the Global Positioning System. Note, since ZIP codes are not specifically designed to be polygons (they are linear postal delivery routes) a given calculated internal point could be well away from the addresses it represents such as addresses clustered along an arc. An example would be addresses along a long arc-shaped street. Also, the file doesn't have ZIP Codes for completely commercial areas or for places with non-city-style addresses (most of the rural areas). ______________________________ Q18: Why am I coming up with gaps in coverage when I try to use TIGER/Line files to create ZIP Code polygon coverage for an area? There are a variety of reasons why you're having this problem. First, we don't have complete ZIP Code coverage in TIGER because we don't have complete address coverage for the entire country. We only have city-style addresses in our data base. P.O. boxes and rural route addresses aren't particularly useful to us for taking the census. We have to use the more traditional "knocking on the door" approach to insure that we have complete coverage. This means our address, and therefore ZIP Code, coverage is not good in the rural areas. A more basic problem is that ZIP Codes were not developed as polygons by the Postal Service, but as a way to manage mail carrier routes. This means that they are really a collection of linear features (carrier routes) at best. Many, particularly in urban areas, can be encompassed neatly by an imaginary polygon. That can't be done easily (or at least accurately) in many other areas, particularly rural. In rural areas there is not necessarily a complete assignment of all land area to one or another post office. By that I mean, a ZIP Code is really a point feature (assigned to a post office, really a building). It may provide some, or no, house delivery service. People can more or less go the one that is closest or most convenient for other reasons to get their mail. The ZIP Code maps produced by mapping companies aren't being made using an authoritative cartographic boundary file coming from the USPS (in our dealings with them we haven't found one). They are the result of these companies making their own judgments and using a variety of sources to come up with an unofficial map. _________________________________________________ Q19: How did you calculate the latitude and longitude for my town since your information puts it at a point that is actually outside of town? The lat/long for each place was a calculated with reference to the legal boundaries of the entity as of the 1990 census and 2000 census respectively, not to the center of a collection of buildings (like the central business district). The calculations were done at that time on a computer using the boundary lat/longs, not by sending people out to each place with a GPS receiver. The resulting point is the approximate geographic center of the polygon making up the legal entity. Whether that is actually useful to anyone is an individual matter. The reason we created these files (they exist for several levels of geography) was for various data analysis and thematic map presentation applications. They provided us a convenient way to link the statistical data being reported for these entities to a geographic coordinate location. They are useful at larger scales of analysis or presentation, for example at the state/national level for place or county coordinates. We put these 1990 census and census 2000 Gazetteer files on site for downloading because people have asked for copies. Note that the legal boundaries and their relationship to the built-up area of a place are local responsibilities. We get the boundary information directly from the local governments. As for the precision of the lat/long coordinates, we recognize that the accuracy of the coordinates is not as good as the precision implies. The extra precision is useful to us for our processing operations by giving us a mathematical way of separating and keeping in order closely spaced features (roads, boundaries, etc.). ______________________________________________ Q20: Why are your products not free. Why do they cost so much? On the issue of product costs, a number of forces are at work. There are a variety of costs associated with any given product such as processing the data into the appropriate form, developing documentation, reproduction, sales/distribution, and customer support. How much of these costs we are required to recover in the price of the product is determined by policies passed down from above, from any level up to the White House. These policies can vary from year-to-year and the cost of each product reflects the policy in effect at the time that it was produced. In most cases we have been obliged to recoup the reproduction/media costs and some portion of the development and after-the-sale support costs. As far as the philosophy on what should be free and what should not, there is no single widely accepted view on what is correct. One argument made is that citizens have already paid for these products with their taxes and they should be free. Another point of view is that the general public shouldn't have to subsidize products that only a very small minority of people have any interest in - let them pay the full cost. The prevailing climate these days seems to be to recoup more of the costs from the individual users. In fact, a recent review of our pricing by a private accounting firm coupled with an interpretation of various regulations is directing us toward complete recovery of all costs associated with each product through the price of that product. In most cases this doesn't include the cost of collecting the data or the basic processing since that is typically covered by a direct appropriation or funds from another government agency. It generally means only those costs incurred to produce a product for public distribution, sales costs, and customer support. _________________________________________________ Q21: What format do you use for your latitude and longitude coordinates? The TIGER data base stores its latitude and longitude in decimal degrees because it's easier for our internal operations. Procedure for converting decimal degrees into Degrees, Minutes, Seconds: Decimal degrees value: 37.427916 Step 1 Degrees = whole number part of decimal degrees Degrees = 37 Step 2 Remove the whole number part of the decimal degrees number 37.427916 - 37 = .427916 Step 3 Multiply the remainder from step 2 by 60 .427916 * 60 = 25.67496 Step 4 Minutes = whole number part of results from step 3 Minutes = 25 Step 5 Remove the whole number part of the decimal number from step 3 25.67496 - 25 = .67496 Step 6 Multiply the remainder from step 5 by 60 .67496 * 60 = 40.4976 Step 7 Seconds = whole number part of results from step 6 Seconds = 40 Or if you want decimal seconds, then seconds = results from step 6 Seconds = 40.5 So decimal degrees 37.427916 = 37 Degrees, 25 Minutes, 40.5 Seconds. Procedure for converting Degrees, Minutes, Seconds into decimal degrees: Degrees, Minutes, Seconds value: 37 Degrees, 25 Minutes, 40.5 Seconds Step 1. Decimal degrees = Degrees + (Minutes/60) + (Seconds/3600) 37 Degrees, 25 Minutes, 40.5 Seconds = 37. + (25/60) + (40.5/3600) 37. + .416666 + .01125 So 37 Degrees, 25 Minutes, 40.5 Seconds = 37.427916 in decimal degrees. _______________________________________________________________________ Q22: How accurate are the TIGER/Line coordinates? The Census Bureau's mission to count and profile the Nation's people and institutions does not require very high levels of positional accuracy in its geographic products. Its files and maps are designed to show only the relative positions of elements. Coordinates in the TIGER/Line files have six implied decimal places. The positional accuracy of these coordinates is not as great as the six decimal places suggest. The positional accuracy varies with the source materials used, but at best meets the established National Map Accuracy standards (approximately +/- 167 feet) where 1:100,000-scale maps from the USGS are the source. The Census Bureau can not specify the accuracy of feature updates added by its field staff or of features derived from the GBF/DIME-Files or other map sources. Thus, the level of positional accuracy in the TIGER/Line files is not suitable for high-precision measurement applications such as engineering problems, property transfers, or other uses that might require highly accurate measurements of the earth's surface. Despite the fact that TIGER/Line data positional accuracy is not as high as the coordinate values imply, the six-decimal place precision is useful when producing maps. This precision allows you to place features that are next to each other on the ground in the correct position, relative to each other, on the map without overlap. We are in the beginning stages of a multi-year process to improve the spatial accuracy of the features in the Census TIGER database and the address information in the Master Address File (MAF). Currently, the Census Bureau's Regional Office staff are updating address information based on locally acquired sources. For more information about the MAF/TIGER Accuracy Improvement Project, go to: http://www.census.gov/geo/mod/maftiger.html _______________________________________________________________________ Q23: Have there been changes in the 1992, 1994, 1995 and later versions of the TIGER/Line files? The format and structure of the TIGER/Line files have changed between the 1992 and the 2002 versions. New record types have been added, and some record types have been deleted. For information on the changes that occurred in the 1994, 1995, 1997, 1998, and 1999 TIGER/LineŽ files refer to Appendix C of the technical documentation. For changes to post-1999 TIGER/Line files, read the Introduction of the most current technical documentation at: http://www.census.gov/geo/www/tiger/ _____________________________________________________________________ Q24: When I enter the lat/long coordinates of my house from my GPS receiver, the TIGER Map Service map pin is shown in the wrong position. There are two possible reasons for this: First, your GPS receiver may be using a different datum (basically the starting reference for the latitude and longitude) than we are using for the data in the TIGER Map Service (1990 decennial and 1998 vintage TIGER/Line). Until the 1995 version of the TIGER/Line files, we used NAD 27. Starting with the 1997 version we changed to NAD 83. The difference between these datums can be as much as 100-200 meters within the continental US. Most GPS units can be programmed to display lat/long results in NAD-27 (or any one of a number of other datums). Second, our map data comes from a variety of sources, mainly the US Geological Survey's 1:100,000 topographic maps. The map accuracy standards (very simply stated) for those maps allows a maximum positional error of 167 ft. See FAQ 2 for more details on this. Other sources include hand annotations to update maps which were not done with surveying precision. _____________________________________________________________________ Q25: What was the datum for the source material from which TIGER was built? Is there a document that describes all the details of the process of creating the TIGER data base? TIGER was never designed (or funded) to be a high precision network because we don't need such precision and it was compiled from a variety of sources. Some source material was referenced to a datum and some was not. We did not keep records of the source's datum. We felt that the potential distortions introduced were not enough to cause us problems for our uses of the data so we did not expend resources to reconcile them. In most cases that assumption proved correct. That means any search for the one true universal datum used in building TIGER/Line is fruitless. From what ever source, the data used to build TIGER was digitized into lat/long coordinates with no stated projection. From the original building of TIGER, and during the ensuing 10 years of updates, any given area could have been compiled from several sources, 1:100,000 USGS DLGs, topo quads in various scales, local maps, aerial photography (by contractors), our DIME files (not originally intended for mapping) and rough sketches by field staff. We used the best materials available within our timing, operational, and budget constraints. Our requirements were that the features were properly named, in the correct relationship to each other, and reasonably accurate in scale. Our field staff need to be able to find and identify features on the ground which does not require maps of engineering precision. When visually matching maps of the same area made from TIGER data with maps made from other, higher precision, sources one could easily see some parts with very close agreement and others with the TIGER features shifted/skewed from the more accurate source. TIGER was conceived and developed in the 1980's in preparation for the 1990 Census. It was a monumental task (even bigger than we anticipated) and nothing like that had ever been done before, so we broke new ground in this effort. It was not done in a vacuum, as we had input from the private sector and elsewhere in government. The critical task, in which we could not fail, was to get an automated national mapping system in place in time to support the 1990 Census. We purposely did not have the old manual system to fall back on in order to force ourselves to get it done. In other words, we were working without a net. This required some compromises of what would have been nice to have in order to get done what was critical. We recognize the limitations of TIGER data for high precision users, however, there is no one piece of undocumented information that will allow a user to overcome the limitations of those compromises. It was also done in a time before the widespread public use of GPS technology. Not many people inside or outside the Census Bureau anticipated the scale of the impact of TIGER to applications beyond the Census. For those interested in the development of the original TIGER data base and it's conceptual underpinnings several journal articles have been written on the subject. A sample of publications where articles appear are: Cartography and Geographic Informatiom Systems, Vol. 17, NO. 1 (1990), Government Information Quarterly, Vol. 7, NO. 3 (1990) and Government Publications Review, Vol. 13. They should be available. They might be available through your library directly or through an inter-library loan. From a practical standpoint, these articles won't tell a user the datum of the original source material for a given piece of geography, nor will they cover the hundreds of operational details and decisions that went into the development, and determined the complexion of the final product. Such a document does not exist. In a continuous operational environment where resources and time are limited, and where product production is the priority, such retrospective case history documentation doesn't get done. The documentation provided with TIGER/Line, and on our web site, is intended to document the files as they exist (content and format) with caveats about their limitations but not many details of their development. We state in Chapter 5 (Data Quality) of the technical documentation that we used a wide variety of source materials in building TIGER and list most of these types. We also note the limitations related to positional accuracy. This information should alert the potential user that questions about the one source datum used, or the one uniform statement of positional accuracy, are not appropriate for the TIGER data set. It was, and still is, designed to meet specific operational needs and not as a general purpose digital data base. Luckily it happens to meet many, if not all, outside user needs. _____________________________________________________________________ Q26: Why is the 2002 TIGER/Line file called 2002 when it was released in 2003? The year noted in the version of the TIGER/Line file normally represents the vintage of the boundaries in the file. Thus, the 2002 TIGER/Line file contains the boundaries for governmental units as of January 1, 2002 (this is the vintage of the boundaries in the fields called "current"). The "current" governmental unit boundaries in the 2002 TIGER/Line files represent January 1, 2002 boundaries as reported in the 2002 Boundary and Annexation Survey. These boundaries are subject to correction before the issuance of the 2003 TIGER/Line files. _____________________________________________________________________ Q27: What datum was used for Hawaii and the Pacific Island Areas in the TIGER/Line Files? For Hawaii and the Pacific Island Areas, the Census Bureau used a variety of sources for building the original digital file in the late 1980s. Neither the specific identities of each of these sources nor their datums were recorded. The information that does exist for this operation indicates that the current USGS topographic quadrangles and/or Defense Department maps were typically, though not necessarily exclusively, used as sources. These would have been based on local datums, however, the Census Bureau does not have information specifically identifying these datums. Such information was not needed for Census Bureau mapping operations when the TIGER database was created for these areas. _____________________________________________________________________ Q28: Is there an equivalency or comparability data product that relates the relationship between Census 2000 ZCTAs (ZIP Code Tabulation Areas) and U.S. Postal Service 2000 ZIP Codes? The Census Bureau is not planning to produce a 2000 ZIP Code to 2000 ZCTA relationship file. We created the ZCTAs specifically to address the inadequacies of ZIP Codes for census data tabulation. Therefore, we see no practical benefit in diverting resources to develop a linkage from ZCTAs back to these ZIP Codes. The relationship between ZIP Code and ZCTA can be determined fully only by comparing individual block-geocoded addresses to the ZCTAs. This process is quite involved. Some examples of why the process can become quite involved are as follows: 1. ZCTAs follow the census block boundaries. In contrast, U.S. Postal Service ZIP Codes serve addresses with no correlation to census block boundaries; therefore, the area covered by a ZCTA may include mailing addresses associated with ZIP Codes that are not the same as the ZCTA. 2. A ZCTA may include a mailing address with a unique or Post Office box ZIP Code that is ineligible to become a ZCTA. Addresses with Post Office box ZIP Codes generally cluster around a post office, but they may be widely scattered across several ZCTAs. Consequently, the relationships that exist between ZCTAs and ZIP Codes can become quite complicated so that within the boundaries of a single ZCTA there may exist several ZIP Codes; likewise, within the boundaries of a single ZIP Code, there may exist more than one ZCTA. 3. Some addresses included in the census and used to define ZCTAs (typically in rural areas) have incomplete or, in some cases, no mailing ZIP Code thus making it difficult to determine the full extent of the relationships between ZCTAs and ZIP Codes._ _____________________________________________________________________ Q29: Is there an equivalency or comparability data product that relates 1990 Census Tracts to Census 2000 Census Tracts? 1990 Census Blocks to Census 2000 Blocks? The Census 2000 files are called Relationship files - Census 2000 Block Relationship, and Census 2000 Tract Relationship Files. The files are linked from the Census 2000 Geographic Products and Information page: http://www.census.gov/geo/www/census2k.html You can download the files from the Web site. At some time in the future, files will be available on CD-ROM. _____________________________________________________________________