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Standard Decennial Census 2000 Products

How to Transfer Population Counts Released from 2000 Census to your TAZs

The "Summary File 1" (SF1) is currently being released by the Census Bureau on a state-by-state basis from June 13, 2001. 

SF1 contains the 100-percent data, which is the information compiled from the questions asked of all people and about every housing unit. Population items reported include sex, age, race, Hispanic or Latino, household relationship and group quarters. Housing items include occupancy status, vacancy status and tenure (owner occupied or renter occupied).

There are 171 population tables (identified with a "P ") and 56 housing tables (identified with an "H ") available at the geographic detail of Census Blocks. In addition there are 59 population tables with detailed race and ethnic origin available at the geographic detail of Census Tracts (identified with a "PCT ") for a total of 286 tables.

For major race and Hispanic or Latino groups, there are 14 population tables and 4 housing tables shown down to the block level, and 4 population tables shown down to the census tract level.

You can obtain SF1 data in three different ways:

1. Census Bureau FTP site:

http://www2.census.gov/census_2000/datasets/Summary_File_1/

This FTP (File Transfer Protocol) application is intended for experienced users of census data, compressed files, and spreadsheet/database software. Due to the size of the files, the FTP user should have a fast file transfer capability. Data are arranged in the FTP site by State.

Each state directory provides all files available for the identified state. Once uncompressed, the data are in a flat ASCII format. The geographic file is in a fixed-field format; the thirty nine data files are in comma delimited format. No software is provided. Users of the FTP application need to unzip the compressed file after downloading, then import it into the spreadsheet/database software of their choice for data analysis and table presentation.

2. American FactFinder (AFF) (http://factfinder.census.gov)

Using American FactFinder, individual tables can be downloaded in a text delimited or comma delimited format.

3. CD-ROM

For users without immediate need for the data, CD-ROMs containing the data and access software are scheduled for shipping shortly after the state file release. They can be ordered from the Census Bureau's Customer Services Center at 301-457-4100.

This document describes how to convert the block data from the SF1 to your TAZs.

I worked on Windows NT, however the process should work on Windows 95, 98, or 2000.  For Unix users, I have a small note at the bottom. Please note that this is *a* method.  There may be far better methods than this.  If you know of any other methods, or have written code to automate the transfer, please let us know.

Here are some general steps in a PC environment:

There are 40 files that need to be FTPed from the site for each state.  I attempted to convert CB files to a GIS Platform, specifically Arcview.
 
Step1. Obtain 2000 Census Block Shape files for your counties.

For any county or state download the shape file for block data and TAZ data from ESRI's website (http://www.geographynetwork.com/data/tiger2000/).  Unzip these files, and keep them in a specially created folder.  I created a folder called d:\VA_sf1_Data, and saved the extracted shape files as 2000blocks.shp and 2000Tazs.shp.

Step2. Obtain the SF1 files for the same counties as Step 1.

FTP the 40 SF1 files from the CB ftp site at http://www2.census.gov/census_2000/datasets/Summary_File_1/

For example, for Virginia, the geographic header file is vageo_uf1.zip, and the data files are va00001_uf1.zip through va00040_uf1.zip.

Step 3. Convert the uf1 files to dbase format.

First, Unzip the zip files you obtained in step 2 using Winzip. These files need a bit of massaging before import to Arcview.

Step a:

The geographic header file (vageo.uf1 or xxgeo.uf1) is a flat ASCII file.  The fields most of us are interested in are:

  1. The State and County FIPS.
  2. The Tract
  3. The Block
  4. The Summary level field (SUMLEV).

To convert the flat file into something that can be used for linking fields, you will need to know where (or at which character) a record/field begins and ends.  This can be obtained in chapter 2 (Figure 2-5, pages 7 through 25) of the file layout document http://www2.census.gov/census_2000/datasets/Summary_File_1/0Technical_Documentation.pdf.

For example:
You can open a new project under MS Access. You may need to rename the uf1 file as a .txt file before beginning this process. Import the xxgeo.uf1 or txt (in this case vageo.uf1 or vageo.txt) file by using the Table Import Wizard, and specify exactly the 18th marker to the 25 marker for the "logical record" which is the key between the geographic header file and the data files.

Note to Database and Spreadsheet Users: Please note that most databases and Spreadsheets handle only 256 fields of information. You have to devise way of organizing tables that are of most interest to you.

The Summary level field (SUMLEV) is between the 8th and 11th marker. (Meaning that the record begins at 9 and is of 3 characters, so it ends at 11th marker).
The State and county FIPS are between the 29 and 34 markers. (Meaning that the record begins at 30 and is of 5 characters, so it ends at 34).
The Tract is between the 55 and 61 marker. (Meaning that the record begins at 56 and is of 6 characters, so it ends at 61).
The block is between the 63 marker and the 66 marker.

Once the table is imported into Access, you can either

  1. Query for a Summary level of your choice. And
  2. Query for a county of your choice.

Note on the summary level field (SUMLEV): For SF1, there is only one SUMLEV field with block information on it (101). So, if you imported only the fields that have block, tract, county, and State FIPS, you can aggregate these in any way they want later, b'coz the block is the lowest atomic unit.

Blocks are unique within tracts. Even if they are duplicate records, the data must be the same for the duplicate records. So, for a given county, if you concatenated State, County, Tract, and Block field in the geographic header file, you *MUST* be able to join it to a similarly concatenated "State-County-Tract-Block" field in the geography network shape file. I did this for PL data, and it worked great. Please not that this process will work only for block level data. It will NOT WORK for data released at the tract level, block grouplevel etc. This is because tracts and block groups may be split by Places and County Sub-divisions. In these cases, it is best to use the SUMLEV field, and query for the exact geographic hierarchy. For example, if you needed all tracts within a county, you would query for SUMLEV = 140. (State-County-Tract).

For a list of summary levels available, refer to page 4-1 of the technical documentation http://www.census.gov/prod/cen2000/doc/sf1.pdf.

In MS Access use File - Export option to save the table to a dbase file.

I called the geography file as va_geography.dbf and saved it in the folder d:\VA_sf1_Data

Step b.

The data files are fairly straightforward to convert as they are comma delimited.
va00001.uf1.zip:  The file is in a convenient .csv format, and can be easily imported to access and converted to a dbf.  The fifth field in this file is the "logical record key" - a field you can use for connecting the data with the geographic dbase file developed in step a.

I named the data file as va_totalcounts.dbf and saved it in and saved it in the folder d:\VA_sf1_Data.

All the data files are formatted in the same way. For your convenience, an excel file with the headers for the CSV file is posted at: http://mcdc2.missouri.edu/data/sf12000/Tools/sf1combo.xls

You can import these into Access and give them some headers that are more recognizable for you.  Export these as DBF too.

Note: In some cases, you may have trouble performing Step 3 in MS Access. This may be due to the way your MS Office is set up. Contact your System Administrator, or someone that knows MS Access really well, when you are unsure of anything in Step 3.

Step 4: Link the shapefile and the datafiles in Arcview

Now, all that remains is to open the shape file, and the data tables in Arcview, create common "join fields" and link/join them together.

Step a.

Open a new Arcview session, and add the block theme you downloaded in step 1 (in my case 2000blocks.shp) as a theme.  Also, add the three tables developed in Step 3.  You will notice you can "join" the geographic header file and the data files easily in Arcview.  I needed only total population counts, so I had only two tables to join (va_geography.dbf, and va_totalcounts.dbf).  I used "logical record field" as the key field to join the two tables. Save the new table as va_counts.dbf

Step b.

The block theme obtained in step 1 (2000blocks.shp) has an attribute table where the state fips, county fips, tract, and block number are concatenated into a single field.  

So to join the shape file to the data file, we need to concatenate the fields containing the statefips, countyfips, tract, and block in the new va_counts.dbf obtained in step 4a.  This can be then connected to the corresponding field in "Attributes of 2000blocks.shp"

Once the data are in Arcview, you can turn on the geo-processing wizard and summarize the data by TAZ, or by Tract easily. To obtain tract level data, Intersect the block shape file with the TAZ shapefile.

Then go to view and dissolve the block shape file on TAZ, Tract or anything else.  This is the reason I added TAZ as an import item in step 1.  You can add other fields you are interested in summation, or geography.

Note for UNIX Users:

You can follow most of the steps outlined for PC users.  You may have to save your files as comma delimited and import them as .txt files into Arcview.  The steps that used Microsoft Access are basically far easier in a UNIX environment.  For example, for the geographic header file, you can use shell scripts or simple "cut" and "paste" commands specifying the exact start and end points for fields (obtained from the file layout manual).  The rest of the process must work.

Note: This note was sent as e-mail to the CTPP listserve. For further questions on converting SF1 data to your TAZs, please contact your local Census State Data Center. To locate the SDC closest to you, please visit http://www.census.gov/sdc/www/

Updated: 05/05/2011
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