Each record on a summary file contains totals for a single geographic location and the geographic codes that describe the location. For example, in 2000 the record with totals for Bronx County will have codes that indicate the state (36-NY), county (05-Bronx), MSA/CMSA (5602 NY-NJ-CT-PA) and PMSA (5600 NY-NY). There also is a code that indicates that the data on the record represents totals at the county level and this code is called the "summary level." For example, on SF3 in 2000 the record that reports county totals for the Bronx would have the geographic codes listed above plus a summary level code of 050 to indicate the totals are for county. A record with totals for a tract in the Bronx would contain the same geographic codes for state, county, MSA, etc. plus a code for tract number and a summary level code equal to 140.
Usually with graphical interfaces to summary file data, the codes are transparent to users. With American FactFinder the summary levels are presented as choices in a list of named levels of geography. This is somewhat true of the interfaces on CD-ROM and DVD versions which also have menu-based access to the data. On these products, data from one summary file can be divided among a number of physical discs and the basis for the division is summary level.
When using the ASCII versions, summary levels also are the basis for dividing a single summary file into A, B, C, etc. parts of the file.Within any one part, a user will use the values in summary level variable to select records for a particular geographic level. Users must consult the technical documentation to see what values to test for.