geo: link generator

What a geo: URI is

RFC 5870 defines geo:latitude,longitude — a map-app-neutral way to point at a place, as opposed to a link into one particular company's map product. Optional parts are an altitude, an uncertainty radius (;u=) in metres, and a label.

Latitude first, and the check that catches the swap

Latitude runs -90 to 90 and longitude -180 to 180. Transposing them is the single most common coordinate error, and past 90 it is detectable — so a latitude out of range is reported here rather than quietly emitted as a point in the ocean.

Six decimal places is the useful limit

The sixth decimal of a latitude is about 11 centimetres. Consumer GPS is accurate to several metres, so anything beyond six digits is noise — and in a QR code it is noise that can push the symbol to a larger version. Coordinates are trimmed accordingly.

Support is uneven, so there is a QR code

Android handles geo: well and offers the user a choice of map app. Desktop browsers largely ignore it. A phone camera pointed at the QR code above works everywhere, which is usually the point of a location link in the first place.