Originally Posted by KerryIrons

It may well be that you can't fathom it. That doesn't mean it isn't real. If you work with RideWithGPS to map and record routes, they have all that elevation data built in. They use Google Maps and OpenStreetMap as two of the choices in their map data, but their elevation profiles come from Google Maps, which shows the elevation changes in detail. That data is there before you ever get on the bike, so no need for either barometer or GPS input. It's one thing to ask questions because you don't know or don't understand, but it's another to be wrong and yet be sure you are right.