These migration flows are derived from the household and group quarter locations sampled in the American Community Survey (ACS) and the responses to the migration questions on the questionnaire.
They are period estimates that measure where people lived when surveyed (current residence) and where they lived 1 year prior (residence 1 year ago). The data are collected continuously over a 5-year period in order to provide a large enough sample for estimates in smaller geographies. The flow estimates resemble the annual number of movers between counties for the 5-year period data was collected.
The flow files produced are:
For each dataset starting with the 2006-2010 5-year ACS, the flow files have been crossed by selected characteristics. A characteristic will not be reused in overlapping 5-year ACS datasets. For instance, age was one of the characteristics for 2006-2010. Age flows will not be produced again until the 2011-2015 flows. These flows with characteristics are subject to suppression for disclosure avoidance purposes. County and county/MCD flows are suppressed if they consist of only one or two people in different households or group quarters. Complimentary suppression is used for the MSA flows.
Characteristics are not crossed with one another, and their universe may vary from one another and the universe for no characteristics, population 1 year and over.
The characteristics are:
The flow statistics are:
Besides the flow files, there are supplemental statistics files that provide summary statistics by mover type (e.g., nonmovers, movers to a state, movers from abroad). These flows crossed by characteristics are also subject to suppression. For the estimates based upon the population of the county 1 year ago, there must be at least 50 unweighted cases for the estimates to be shown.
To properly render flow statistics, both a reference geography and a second geography need to be included. Supplemental statistics only need a reference geography. The county-to-county flows are also available through an interactive mapping tool, the Census Flows Mapper.
For more information, please visit the Migration/Geographic Mobility page.
Unlike previous releases, the current migration flow release does not cross include characteristics. Instead, it only includes counts.