Electronic Product User Note

Accessing 1990 Census CD-ROM data in dBase III+^™ format directly

The procedure below is a quick guide to accessing 1990 census data files in dBase^™ III Plus format directly (without using the DOS software provided on the CD-ROM discs) with database management software (DBMS) such as Microsoft Access^™.

• Use tables.dbf or the Subject Locator section (document\sub_loc.asc on disc) of the file documentation to get table numbers for demographic tables of interest. Use tables.dbf or the Table Matrix section (document\tbl_mtx.asc on disc) to see all of the categories (data items) in that table.
• Use tables.dbf or the How to Use this File section (document\howtouse.asc on disc) to find the number of the data file that contains a specific demographic table (see above).
• Use the Summary Level Sequence Chart section (document\howtouse.asc on disc) for area type record selection criteria (codes for SUMLEV)
• Open file number "00" (file containing a complete list of geographic identifiers) to generate area lists (such as a list of county names and codes) if necessary by using the appropriate area type (summary level) code.
• Open and query data file containing desired demographic data tables
• Use the unique key field LOGRECNU to link each data file back to the geographic identifier file (00 file) to obtain more geographic identifier information for specific areas if necessary.

What summary level code should you use?

There may be cases where two or more summary levels look alike. Look at the following example from 1990 Summary Tape File 3A:

Reading from right to left, if any area type right of a dash can cross the boundaries of any area type left of that dash, the summary level (area type for which statistics are compiled) will include area parts. Since a Census Tract or Block Numbering Area (BNA) can cross place or county subdivision boundaries, SUMLEV="080" will contain Census Tracts or BNAs whose data are split into multiple records ; one for each part of, in this case, a Census Tract or BNA. It is necessary to use the geographic identifier field for each element in the complete summary level description (see above) to uniquely each specific area.

There are no duplicate records in the data set. If you link any data file number back to the first segment (the "00" file) on LOGRECNU (logical or physical record number), at least one field will be different. The fields GEOCOMP and URBANRUR are the most common examples of this. See the Data Dictionary section (document\iden_ftn.asc) for a description of the geographic identifier fields.

Source: U.S. Census Bureau, Administrative and Customer Services Division, Electronic Products Development Branch
Last Revised: November 01, 2007 at 04:32:05 PM

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