How address formats differ between countries
The order of a street, a house number, a city, and a postal code is not universal. Getting the format wrong for a given country is one of the most common causes of failed geocoding.
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#standards
Coordinate reference systems: why WGS84 is the default
Every set of coordinates is defined relative to some model of the Earth's shape. WGS84 became the default for GPS and web mapping for practical reasons worth understanding.
ISO 3166-1 and 3166-2 codes, and where they get confusing
Country codes and subdivision codes look simple until you hit the exceptions. Here is what ISO 3166-1 and 3166-2 actually cover, and where confusion creeps in.