GPS in Cities: Tall Buildings, Reflections and Urban Canyons
Understand multipath and satellite visibility problems that can make location and speed readings jump in dense cities.
Tall buildings can block part of the sky and reflect satellite signals off glass, concrete and metal. In a street surrounded by high buildings, the phone may receive both direct and reflected signals. This environment is often called an urban canyon, and it can produce position jumps even when a person or vehicle follows a straight road.
What multipath means
A reflected signal travels a longer path than the direct signal. If the receiver uses that reflected signal in its position calculation, the computed location may be displaced. The phone's location provider may reject some poor measurements, but a website cannot control the receiver's internal algorithms.
Why speed is affected
Speed can be estimated from successive positions or from a speed field supplied by the device. If positions jump from one side of a street to another, a simple distance calculation can invent movement that did not happen. If a device provides a separate speed estimate, that value may behave differently, so the exact issue depends on the implementation.
Practical troubleshooting
Compare performance on an open road or field and in the city street, while stationary and without handling the phone while driving. Keep the phone's sky view as clear as practical. If the accuracy estimate worsens between buildings, treat the displayed speed and trip distance cautiously rather than attempting to compensate with a made-up correction factor.
Route planning implication
A plotted track can drift across buildings or appear to cut corners. This does not necessarily mean the person travelled through a wall; it can reflect uncertainty between fixes. For a route record, look at the overall path and conditions instead of treating each coordinate as a survey point.
Frequently asked questions
Why does GPS jump across a street?
Blocked sky and reflected signals can shift the computed position.
Can software remove all urban GPS error?
No. Filtering can reduce some noise but cannot reconstruct information the receiver never obtained.
Technical references
These references explain the underlying browser and positioning concepts. They do not imply endorsement of this website.