Readme File for Detailed Tables (DTs) 1. dt_readme.txtThis readme file is provided to explain the file naming conventions and general content of the downloaded files.When applicable, a second data set specific readme file also is provided to explain potential gaps in the data for the selected geographic areas. In many data sets in American FactFinder (AFF), not all data are available for all geographic areas. The specific reason varies with each data set but in general is due to one of the following reasons:- sampling sizes- population thresholds- geographic thresholds for selected tables Be sure to consult the data set specific readme file when it is provided.2. Detailed Table data files and what they contain. a) File type extensions: The data files are either comma delimited text files or Microsoft Excel (.xls) files. Two types of data files are created:dt__data1. = dynamically produced file with data valuesdt__geo.= dynamically produced file with the geocode values = the unique data set name = the chosen file extension (.txt or .xls)b) Non-iterated Data Files: _data1.A download may contain one or more dynamically produced file(s) with data values. These will be named as dt__data1.,dt__data2. etc. Each data file includes primary keys to link to other data files:GEO_ID: the Geographic IdentifierGEO_ID2: the GIS-compatible Geographic IdentifierSUM_LEVEL: the Summary Level CodeEach data file has a maximum of 250 data columns. When that is exceeded, a new data file is created. Large downloads of many tables will result in multiple data files.c) Iterated Data Files: dt__data001_1.These data sets contain tables that are repeated for Race and Ethnic Groups (REGs) and/or Ancestries, for example, Summary Files 2 and 4 from the Census 2000. Downloads from these data sets will be named as:dt__data001_1.dt__data001_2. dt__data002_1.dt__data003_1. etc. Each file will contain data for one Race or Ethnic Group (REG); the REG is identified by the 3 digit code in the file name *data001*.. Each file will contain no more than 250 columns of data including the keys, therefore, multiple data files may be created for each REG. However, each file will contain data for only one REG. Iterated data files contain 3 primary keys to link to other data files:GEO_ID: the Geographic IdentifierGEO_ID2: the GIS-compatible Geographic IdentifierCHARITER: the 3 digit code that corresponds to the Race and/or Ethnic Group(s) SUM_LEVEL: the Summary Level Coded) Geographic Content File: dt__geo. This file is dynamically produced and contains the geocode values for all of the selected geographic areas. This file can be linked to the various data files by the primary keys of: GEO_ID: the Geographic IdentifierGEO_ID2: the GIS-compatible Geographic IdentifierSUMLEV: the Summary Level CodeThe GEO_ID is used in the American FactFinder application to uniquely identify each geography. A GEO_ID is formed by appending a series of text strings: 3-digit summary level code + '00US' + applicable geocodes. For example, the GEO_ID for Autauga County, Alabama would be formed by appending: '050' + '00US' + '01' (State FIPS) + '001' (County FIPS) to produce: '05000US01001'.The GEO_ID2 can be used by GIS software users who use Census data and need acommon key to link AFF tabular data to TIGER spatial data. GEO_ID2 is a field that contains the applicable geocodes without the 3-digit summary level code and the '00US'.TIP: The file names for *data*.txt and *geo.txt do not uniquely reflect the contents of the file. The same file names will be reused on subsequent downloads with different content. Be sure to modify your files names when downloading multiple times. 3) Refer to the Readme_.txt for more informationThe geographic selections in the *geo.txt file may not have matching data values in the data.txt files. The reasons for this vary by data set. Refer to individual readme files for each data set for further explanation. 4) Data Set Technical DocumentationThe technical documentation is available from the data sets page. Click on the data set radio button and then click on the Technical Documentation link. The data set page can be bookmarked:http://factfinder.census.gov/servlet/DatasetMainPageServlet?_lang=en