The data on residence 1 year ago were derived from answers to Question 15, which were asked of the population 1 year and older. For the American Community Survey, people who had moved from another residence in the United States or Puerto Rico 1 year earlier were asked to report the exact address (number and street name); the name of the city, town, or post office; the name of the U.S. county or municipio in Puerto Rico; state or Puerto Rico; and the ZIP Code where they lived 1 year ago. People living outside the United States and Puerto Rico were asked to report the name of the foreign country or U.S. Island Area where they were living 1 year ago.

For the Puerto Rico Community Survey, people who moved from another residence in Puerto Rico or the United States 1 year ago were asked to report the exact address, including the development or condominium name; the name of the city, town, or post office; the municipio in Puerto Rico (county equivalent) or county in the U.S.; and the ZIP Code where they lived. People living outside Puerto Rico and the United States were asked to report the name of the foreign country or U.S. Island Area where they were living 1 year ago.

Residence 1 year ago is used in conjunction with location of current residence to determine the extent of residential mobility of the population and the resulting redistribution of the population across the various states, metropolitan areas, and regions of the country.

When no information on previous residence was reported for a person, information for other family members, if available, was used to assign a location of residence 1 year ago. All cases of nonresponse or incomplete response that were not assigned a previous residence based on information from other family members were allocated the previous residence of another person with similar characteristics who provided complete information.

The tabulation category, "Same house," includes all people 1 year and over who did not move during the 1 year as well as those who had moved and returned to their residence 1 year ago. The category, Different house in the United States includes people who lived in the United States 1 year ago but in a different house or apartment from the one they occupied at the time of interview. These movers are then further subdivided according to the type of move.

In most tabulations, movers within the U.S. are divided into three groups according to their previous residence: "Different house, same county," "Different county, same state," and "Different state." The last group may be further subdivided into region of residence 1 year ago. An additional category, "Abroad," includes those whose previous residence was in a foreign country, Puerto Rico, American Samoa, Guam, the Northern Marianas, or the U.S. Virgin Islands, including members of the Armed Forces and their dependents. Some tabulations show movers who were residing in Puerto Rico or one of the U.S. Island Areas 1 year ago separately from those residing in foreign countries.

In most tabulations, movers within Puerto Rico are divided into two groups according to their residence 1 year ago: "Same municipio," and "Different municipio." Other tabulations show movers within or between metropolitan areas similar to the stateside tabulations.

The American Community Survey Summary Files include all detailed tables for all geographic areas published by the 2009 1-Year ACS. The main directory of the American Community Survey' s Summary File product release, located within the file transfer protocol (FTP) site, contains documentation about the Summary Files, information pertaining to the United States, each of the individual states, the District of Columbia, and Puerto Rico. The following list outlines the hierarchical geographic levels contained within the Summary File release.

Geographic Component	Summary Level
00, 01, 43, A0, C0, C1, C2, E0, E1, E2, G0, H0, 89, 91-94	010 United States1
00, 01, 43, A0, C0, C1, C2, E0, E1, E2, G0, H0	020 Region1
00, 01, 43, A0, C0, C1, C2, E0, E1, E2, G0, H0	030 Division1
00, 01, 43, A0, C0, C1, C2, E0, E1, E2, G0, H0	040 State2
55-59, 60-62 00	050 State-County3
00	060 State-County-County Subdivision
00	160 State-Place
00	500 State-Congressional District (111th)
00	795 State-Public Use Microdata Area (5%)
00	950 State-School District (Elementary)/Remainder4
00	960 State-School District (Secondary)/Remainder4
00	970 State-School District (Unified)/Remainder4
00	230 State-Alaska Native Regional Corporation
00	250 American Indian Area/Alaska Native Area/Hawaiian Home Land
00	310 Metropolitan Statistical Area/Micropolitan Statistical Area
00	312 Metropolitan Statistical Area/Micropolitan Statistical Area-State-Principal City
00	314 Metropolitan Statistical Area/Micropolitan Statistical Area-Metropolitan Division
00	330 Combined Statistical Area
00	335 Combined New England City and Town Area
00	350 New England City and Town Area
00	352 New England City and Town Area-State-Principal City
00	355 New England City and Town Area (NECTA)-NECTA Division
00	400 Urban Area

Footnotes:

¹Land area, water area, population counts, and housing unit counts for the United States, Regions, and Divisions do not include Puerto Rico.

²State, District of Columbia, or Puerto Rico.

³Parish in Louisiana, Borough or Census Area in Alaska, and Municipio in Puerto Rico; in Maryland, Missouri, Nevada, and Virginia, one or more cities are independent of counties and are treated as statistical equivalents of counties; the entire District of Columbia, which has no counties, is treated as a county equivalent.

⁴Remainder of school districts are published for ACS 5-year data.