A method of estimating a location of a terminal includes measuring a magnetic field value at a location of the terminal, estimating the location of the terminal using the measured magnetic field value, and transmitting the measured magnetic field value and information associated with the estimated location to a server. A method of modifying a magnetic field map includes receiving, from a terminal, a magnetic field value estimated at a location of the terminal, and information associated with a location of the terminal estimated based on the magnetic field value, and modifying a magnetic field map using the measured magnetic field value and the information associated with the estimated location.