When to use it
Event invitations, delivery instructions, a hard to find trailhead or car park, a farm shop down a track, a stall in a large market, a wedding venue. A location code puts a pin on the map with no typing, and a second tap gives turn by turn directions from wherever the person is.
How it behaves on phones
iPhone: the Camera app recognizes geo: and shows an “Open in Maps” banner. Apple Maps opens with a pin at the coordinates. Google Maps is not offered unless the person has changed defaults through a third party scanner.
Android: most Android scanners hand geo: to Google Maps, or show a chooser if several map apps are installed. The pin appears and a directions button is one tap away.
Common mistake
Encoding a Google Maps link copied from the browser’s address bar. Those are often 150 characters of place IDs, zoom levels and view parameters, making a dense code that scans badly. Use geo: or the short https://maps.google.com/?q=lat,lng form. If the goal is a review rather than directions, the place ID belongs in a Google review QR code instead, which opens the write-a-review box.
Gotchas
Order and sign. Latitude first, longitude second, in decimal degrees. North and east are positive, south and west negative. 51.5007,-0.1246 is Westminster; -0.1246,51.5007 is the Gulf of Guinea.
Precision. Four decimals places a pin within about 11 m, enough for a building entrance. Five is about 1 m. Extra digits add characters without adding accuracy your phone can use.
Map URL alternatives. https://maps.google.com/?q=51.5007,-0.1246 opens Google Maps on both platforms, in the app if installed and in the browser if not. https://maps.apple.com/?ll=51.5007,-0.1246 does the same for Apple Maps and redirects Android users to a web map. Both are longer than geo: and depend on the internet, but they let you add &q=Town+Hall for a label.
Size. geo:51.5007,-0.1246 is 19 characters and fits version 1 at level M, 21 modules wide. A Google Maps URL with a label is 50 to 60 characters and needs version 3 or 4.
Offline. geo: works with no signal as long as the map app has the area cached. A maps URL needs a connection to resolve first.
Try it in QR Studio
QR Studio has a Location type where you drop a pin or paste coordinates, and it writes the geo string for you.
Print advice
Level M for invitations and flyers. Use Q or H for an outdoor sign at a trailhead or venue gate where the code faces weather, since a location payload is tiny and the larger code costs little. Print the address or a short “what3words” style description in text as well, for people navigating without a phone.
Try it yourself
Paste coordinates from your map app and see the geo string the code will carry.