Why doesn't GPS work indoors?
GPS was built to solve a different problem: pinpointing a position under open sky, using a clear line of sight to satellites. A building's roof and walls are exactly what it does not expect to be in the way.
- Roofs and walls block the signal
- GPS needs a clear line of sight to satellites. Concrete, steel and low-E glass attenuate or reflect it, and multiple reflections off nearby surfaces confuse the fix rather than simply weakening it.
- Floors look identical to a satellite
- GPS gives you a position on the ground. It has no reliable way to say which of eight stacked floors you are standing on.
- Accuracy degrades from metres to unusable
- A GPS fix that is accurate to a few metres outdoors is often wrong by tens of metres indoors, which is worse than useless for telling someone which door to take.
None of that is a flaw in GPS. It simply was not designed for this problem, which is why indoor navigation uses a different approach rather than a stronger version of the same one.
So what does it use instead?
A floor plan is turned into a graph: a network of points connected by the paths a person can actually walk, in the same shape as a road map is a network of junctions connected by roads. Every point of interest, a room, a desk, a gate, a department, is attached to a specific point on that network rather than floating on top of it as a separate layer.
What that looks like end to end:
The floor plan becomes a graph
Corridors, doorways and open areas become a network of waypoints connected by the paths a person can actually walk. A destination is a point attached to that network, not a separate layer on top of it.
You give it a known starting point
Scanning a QR code at a kiosk or on existing signage tells the system exactly which waypoint you are standing at. No GPS fix, no beacon, just a fixed point that is already known.
It finds a path across the network
The same kind of shortest-path calculation a road-trip planner uses, run across corridors and stairwells instead of streets and junctions.
The route crosses floors where it needs to
A lift, stairwell or escalator is a connection between two graphs rather than a dead end, so a route can span floors as naturally as it crosses a room.
How does it know where you are starting from?
This is the part GPS would normally do, and indoors it is solved more simply than most people expect. A QR code at a kiosk or on existing signage encodes exactly one fact: which point on the network you are standing at right now. Scan it, and the system has a known, exact starting position with no satellite fix and no positioning hardware involved.
That is enough to search for a destination, calculate a route and give step-by-step directions from there. It is a fixed starting point rather than a continuously updating one, and for the large majority of wayfinding, finding a specific place from a known entrance, that is exactly what is needed.
Do you need beacons or Wi-Fi triangulation?
Not for the search-and-route problem above. Where beacons, Wi-Fi triangulation or other positioning hardware come in is a different, harder feature: a live position marker that moves with you continuously as you walk, the way a phone's map app shows your dot moving down a street. That is a real capability some platforms offer, it has a real hardware and maintenance cost, and it is worth asking any vendor to demonstrate rather than assume, since "positioning" and "wayfinding" are often sold as the same thing when they solve different problems.
What changes floor to floor?
A lift, stairwell or escalator is not a dead end in the graph, it is a connection between the graph on one floor and the graph on the next. A route that needs to change floors crosses that connection the same way it crosses any other point on the network, which is also what makes step-free routing possible: request it, and the route uses the lift and ramp connections instead of the stair ones.
Read next: indoor wayfinding explained covers the wider category, and Arabic wayfinding covers what changes when the same graph has to work in a right-to-left interface. Comparing vendors, see how to choose indoor wayfinding software.