Data & Methodology

Every number on ZipLocal Guide traces back to a public, government-produced or open dataset. We don't publish proprietary "scores" or weighted indexes — we summarize cited figures and let you draw your own conclusions.

Geographic backbone

The list of ZIP codes, the city and state each ZIP belongs to, the county, and the centroid latitude/longitude come from the GeoNames postal data dump for the United States. GeoNames is a Creative Commons-licensed open data project that mirrors and consolidates official postal data. Their U.S. file currently contains around 41,500 active ZIP codes covering the 50 states, D.C., and U.S. territories.

For each ZIP, we use the GeoNames-provided centroid as an approximate point location. Because ZIP codes are mail-routing constructs, not census-defined polygons, this point is an approximation, not a property boundary.

Demographics & cost-of-living figures

Population, median household income, median home value, median gross rent, median age, count of unemployed residents, and count of bachelor's-degree holders all come from the U.S. Census Bureau American Community Survey 5-Year Estimates (2018–2022), queried at the ZIP Code Tabulation Area (ZCTA) level via the Census API.

Specifically, we pull these ACS variables: B01003_001E (total population), B19013_001E (median household income), B25077_001E (median value of owner-occupied housing units), B25064_001E (median gross rent), B23025_005E (unemployed civilian labor force), B15003_022E (bachelor's degree count age 25+), and B01002_001E (median age).

The ACS publishes margins of error alongside its point estimates; for readability we display only the point estimate. For ZIPs with very small populations the underlying margins of error can be substantial, and small-area ACS figures should be treated as ballpark indicators rather than precise measurements.

ZIP vs. ZCTA

Strictly speaking, a USPS ZIP Code is a mail-delivery route and a Census ZCTA is a polygon approximating where that ZIP's deliveries are concentrated. The two lists overlap heavily but are not identical: a small number of mail-only ZIPs (post-office boxes, single buildings) have no corresponding ZCTA and therefore no Census demographic figures. On those pages you'll see geographic information but blank or em-dashed demographic fields.

Aggregation

City and state pages on ZipLocal Guide are mechanical roll-ups of the underlying ZIP-level data: total population is summed; medians are reported as the average of ZIP-level medians, weighted equally rather than by population. This is faster to compute than a true population-weighted median but is also a rougher approximation. We flag a more rigorous methodology as a future improvement.

What we don't claim

We do not publish school ratings, crime indexes, or "best places" rankings.
We do not project property values forward or estimate appreciation.
We do not provide individual-level data of any kind. ACS releases are aggregate by design and protected by Census disclosure-avoidance rules.

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