Testing location data with edge cases, not just happy paths
An address in a well mapped city center tells you almost nothing about how your system handles a rural route, a disputed border, or a query near the poles. Test the hard cases deliberately.
Postal code granularity: the UK versus the US versus everywhere else
Ask what a postal code represents and the honest answer is that it depends entirely on which country issued it. There is no international standard for postal code granularity, only a general concept, applied differently everywhere, that a national postal authority defines a code format suited to its own delivery network. The result is wildly different levels of precision depending on where you look.
UK postcodes sit at the fine end of the spectrum. A full postcode, including the outward and inward parts, often narrows down to a single street, a short stretch of it, or in dense areas a small handful of buildings. This makes a UK postcode alone a genuinely useful piece of location data, closer in practical value to a partial address than to a simple area code.
US ZIP codes work at a much coarser level. A ZIP code typically covers a delivery area that can span a substantial part of a town or a chunk of a city, sometimes containing thousands of addresses and covering a meaningful amount of physical area. A ZIP code tells you the general neighborhood or delivery zone, not a specific street, and treating it as equivalent to a UK postcode in terms of precision will lead to bad assumptions.
Other countries fall across the range between these two extremes, and some do not use a numeric or alphanumeric grid at all in the way either the UK or US does. Canada's postal codes are closer to the UK's in granularity, narrowing to a small area or even a single building for high-volume addresses. Many countries use codes that map more to a district or a locality than a coordinate area at all. There is real variation here worth checking per country rather than assuming any one pattern applies universally.
This matters directly for anything that infers location from a postal code. Using only a ZIP code to place a US customer will position them somewhere within a fairly wide area, which is fine for regional analytics and risky for anything requiring finer precision. Using a UK postcode for the same purpose gets you much closer to an exact address, sometimes close enough to be mistaken for one. Building logic that assumes uniform postal precision across countries is one of the more common sources of quiet accuracy problems in international address handling.
Our postal code lookup takes a code together with its ISO 3166-1 alpha-2 country and returns matching coordinates and administrative components, so you can check exactly how tightly a given code resolves before relying on it as a location signal.