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Where Do Emsi’s Region Definitions Come From?

Emsi uses information from the Census Bureau and the United States Post Office to define the regions used in Emsi Data. In some instances, there are several “sources of truth” for region definitions. For example, the Post Office uses ZIP codes to figure out the most efficient mail delivery routes. USPS updates ZIP codes every month. Other entities use other definitions of ZIP codes, which can lead to data sources using different ZIP definitions being out of sync.

Nation/State

Nation and State definitions are stable and undisputed; Emsi does not consult any outside source to define these regions.

County

Like nation and state, county definitions are relatively stable. Emsi updates county definitions by tracking the Census’s Substantial Changes page. Emsi incorporates county changes as they are listed there.

ZIP

Emsi follows USPS’s convention for ZIP codes. USPS publishes a new version of ZIP codes every month, and Emsi uses the latest available definitions with each datarun. USPS ZIP code definitions must be purchased and are available in their Delivery Statistics (DelStat) product.

Census Tract

Census Tracts are generally quite stable and only change in the event of a Census or a county change. Emsi uses census tract definitions from the Census Bureau. Like with counties, we monitor this page for changes and update as new tract definitions are available.

Metro-/Micropolitan Statistical Area (MSA)

MSAs are agglomerations of counties. Metro areas that exceed certain population thresholds are considered micro- or metropolitan statistical areas. Since populations change constantly, MSA definitions change more frequently. Emsi monitors the Census’ Geography Delineations page, where the Census publishes new delineation files whenever an MSA change takes place. Emsi incorporates new MSA definitions as they are published on this site. The “Core based statistical areas (CBSAs), metropolitan divisions, and combined statistical areas (CSAs)” files are the ones used.

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