Satellites send signals, not maps
GPS satellites broadcast information about their locations and the time their signals were sent. A phone or another GPS receiver listens for these signals. The receiver does not normally need to transmit a request to the satellites to determine its position.
Time becomes distance
Because radio signals travel at approximately the speed of light, their travel time provides an estimate of distance. Combining distance estimates from multiple satellites lets a receiver solve for its position. Measurements from at least four satellites are typically needed to determine three-dimensional position and correct the receiver clock offset.
Why accuracy varies
Buildings, trees, terrain, and reflections can make the incoming signals harder to interpret. Atmospheric effects and satellite geometry also matter. Phones may combine satellite signals with Wi-Fi, cellular network information, and sensors to improve the location shown on screen.
The bigger picture
GPS provides positioning, navigation, and timing services. It includes satellites in space, a ground control system, and the receivers that people and machines use. The map you see is a separate software layer built on top of that positioning estimate.
Read the original sources
These sources explain the underlying science or reference facts. Review them when you need more detail or updated guidance.