“It’s fascinating how much complexity and ingenuity is hidden behind the simple act of observing one’s location in a mapping app on a smartphone.”
Interactive demos walk from three landmarks on a toy map to atomic clocks, orbital mechanics and relativistic corrections. Your phone decodes a very weak signal from orbit and turns it into a blue dot. The US military runs the whole system and gives the signal away. Most people never think about it until the dot jumps a block.