Readme File for Quick Tables (QTs) 

1. qt_readme.txt

This 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 is 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. Quick 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:

	<dataset>_data1.<ext> = dynamically produced file with data values
	<dataset>_geo.<ext>= dynamically produced file with the geocode values

	<dataset> = the unique data set name
	<ext> = the chosen file extension (.txt or .xls)


b) Non-iterated Data Files: <dataset>_data1.<ext>

A download may contain one or more dynamically produced file(s) with data values. These will be named as <dataset>_data1.<ext>,<dataset>_data2.<ext> etc. Each data file includes 2 primary keys to link to other data files:

	GEO_ID: the Geographic Identifier
	SUM_LEVEL: the Summary Level Code

Each data file usually contains one Quick Table. If a Quick Table exceeds 250 data columns, a new data file for that table is created. 


c) Iterated Data Files: dt_<dataset>_data001_1.<ext>

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:

<dataset>_data001_1.<ext>
<dataset>_data001_2.<ext> 
<dataset>_data002_1.<ext>
<dataset>_data003_1.<ext>   etc.

 
Each file will contain data one table for each Race or Ethnic Group (REG). For example, a Quick Table download of 4 tables for 4 different REGs will result in 8 separate data files, assuming each table is less than 250 columns. When a table exceeds 250 columns, a new data file is created for that iteration. The REG is identified by the 3 digit code in the file name data001_<n>.<ext>. Iterated data files contain 3 primary keys to link to other data files:

	GEO_ID: the Geographic Identifier
	SUM_LEVEL: the Summary Level Code
	CHARITER: the 3 digit code that corresponds to the Race and/or Ethnic Group(s)  

	
d) Geographic Content File: dt_<dataset>_geo.<ext> 

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 Identifier
	SUMLEV: the Summary Level Code
	
The 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'.


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_<dataset>.txt for more information

The 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 Documentation

The 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