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ZIP list audit

Paste your territory spreadsheet, or open it as a CSV. You get back the ZIPs that sit in two territories, the ones with no area on any map, the ones Excel has damaged, and the ones that cross county or state lines.

Your list stays on your computer. The check runs in this page. The only thing it downloads is a fixed public Census table, the same file for everybody, and nothing you paste or open is sent anywhere or stored.

A column of ZIP codes, and optionally a territory or owner column beside it. Comma or tab separated, with or without a header row, or just ZIPs separated by spaces.

Excel files: save as CSV first. The file is read by this page only.

What each finding means

In more than one territory
The same ZIP is assigned to two owners. Whichever rule picks the winner (first row, last row, whoever saw it first) is a rule nobody wrote down.
No Census area
The ZIP has no ZIP Code Tabulation Area. Usually it is a PO box ZIP, a ZIP for one building or organisation, or a retired or very new ZIP. It is a real ZIP, but it will not geocode to an area or show on a ZIP map, so a territory map built from your list will not show it either.
Leading zero restored
Excel reads 02134 as the number 2134. Every ZIP in New England, New Jersey and Puerto Rico starts with a zero, so a sheet that has been through Excel often has four-digit ZIPs. The audit pads them back to five digits and lists each one it changed, so you can fix the source.
More than one county, or across a state line
The ZIP's area falls in two or more counties, shown with each county's share of its land. Harmless for most uses. It matters when the county decides something: a tax rate, a licence, or a territory agreement written by county. The state-by-state numbers show how common it is where you work.

Where the county data comes from

  • A ZCTA is not quite a ZIP code. ZIP Code Tabulation Areas are the Census Bureau's approximations of ZIP code areas, built by grouping census blocks by the ZIP codes of the addresses in them. USPS ZIP codes are delivery routes, not areas, and the two do not always match.
  • Some ZIP codes have no ZCTA at all. PO box ZIPs, ZIPs for a single building or a single large organisation, and military ZIPs usually have no area of their own, so they cannot be split across counties here and will not match any area in a map.
  • Land share is not population share. A ZCTA with 20% of its land in a second county might have almost none of its people there, or most of them. The shares here measure area, which is what the Census file publishes.
  • Tiny overlaps are included. A ZCTA counts as overlapping a county if the Census file lists any part of it there, including slivers along a road or river. That is why the share with at least 5% of land in a second county is shown alongside.

Source: U.S. Census Bureau, 2020 ZCTA to County relationship file, public domain. Counts use 2020 ZCTAs and 2020 county boundaries. ZIP codes added by USPS since then are not in it, and Connecticut's counties have since been replaced by planning regions in Census data.

When a ZIP list stops being enough

A ZIP list is a fine way to start. MapLogics routes by a boundary you draw or import, or by the address itself, so an address on the far side of a county line in a split ZIP goes to the territory it is actually in, and two territories cannot both claim it without somebody being told. The trial is free and you can import the list you just checked.

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