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.
Why some countries publish better postal code data than others
Ask why postal code lookups are dramatically more precise and reliable in some countries than others, and the answer traces back almost entirely to a single source: each country's own postal authority defines its postal code system and decides how, and how openly, the underlying reference data gets made available. There is no single global body governing postal code data quality, only the general pattern that a national postal authority owns and maintains its own country's format, and countries differ enormously in how they exercise that role.
Some postal authorities maintain highly granular, frequently updated, and openly published reference data, mapping codes down to individual streets or even buildings, and making that data readily accessible for exactly the kind of use case a geocoding service depends on. Others maintain coarser data internally, focused mainly on their own delivery operations rather than on serving as a public reference dataset, or restrict how widely and in what form their reference data can be shared and used by outside parties.
This variation is not a reflection of a country's overall infrastructure quality in any broad sense, it specifically reflects decisions made by that country's postal system about data granularity and openness. A country can have excellent physical mail delivery and still maintain postal reference data that is comparatively coarse or hard to access from the outside, simply because the operational need to deliver mail does not require the same level of published detail that a third-party lookup service benefits from.
The practical consequence is that anyone building on postal code data internationally should expect meaningfully different resolution and reliability from one country to the next, and should design accordingly rather than assuming uniform behavior. Where postal data is granular, it can support genuinely precise geocoding on its own. Where it is coarser, it is better treated as one supporting signal alongside a fuller address, rather than as a sufficient location identifier by itself.
Checking real results for the specific countries relevant to your application is far more useful here than any general assumption, since the gap between the best and weakest supported countries can be substantial. Our postal code lookup returns matching coordinates and administrative components for a code and its ISO 3166-1 alpha-2 country, and testing it directly against representative codes from each country you actually operate in will tell you far more about what to expect than any general statement about postal data quality worldwide.