1) Geo Tagging is a fantastic concept. Satellite signals can't reach in closed places like malls etc...
2) In public commutes like buses & trains, why should every one turn on their GPS ? All of them share same position.
3) GPS signal is very week. Enabling GPS consumes lots of Mobile phone battery GPS takes nearly 20sec to identify GeoPosition
A solution can be: decoded Geo Position can be shared on FM channel. This will be pretty quick to identify the location. Consumes very less battery.
A mall can always send a fixed GeoPosition. (People can use for <Location based services> or <geoTagging thier photos>)
A Bus can have a single GPS receiver and send the GeoPosition on FM channel.
A train can do the same as bus for each coach
An alternative solution can be WiFi:
If a mall is providing free WiFi, decoded Geoposition can be transmitted to the devices over wifi signals.