A method of estimating the position of an electronic device, comprising: receiving an observation including the identity of at least one wireless transmitter detected by the device at the position to be estimated; comparing the observation with a plurality of records, each record comprising the identity of one or more wireless transmitters and a corresponding position, the position being based on a location or set of locations at which the one or more transmitters were detected; detecting a first match between the observation and a first record, the first record comprising a corresponding first position; determining a quality characteristic of the first match; determining a first indication about a first device which contributed to the first record; detecting a second match between the observation and a second record, the second record comprising a corresponding second position; determining a quality characteristic of the second match; determining a second indication about a second device which contributed to the second record, wherein the second indication is different from the first indication; and estimating the position of the electronic device based on at least one of the first and second positions, depending upon the first indication, the quality characteristic of the first match, the second indication and the quality characteristic of the second match, wherein the quality characteristic of the first match and second match comprises a measure of how specific each match is, and wherein when the first and second indications suggest that the first device is more closely related to the electronic device than the second device: if the second match is more specific than the first match, then the estimation of the position of the electronic device is based preferentially on the second position; and otherwise, the estimation is based preferentially on the first position. receiving an observation including the identity of at least one wireless transmitter detected by the device at the position to be estimated; comparing the observation with a plurality of records, each record comprising the identity of one or more wireless transmitters and a corresponding position, the position being based on a location or set of locations at which the one or more transmitters were detected; detecting a first match between the observation and a first record, the first record comprising a corresponding first position; determining a quality characteristic of the first match; determining a first indication about a first device which contributed to the first record; detecting a second match between the observation and a second record, the second record comprising a corresponding second position; determining a quality characteristic of the second match; determining a second indication about a second device which contributed to the second record, wherein the second indication is different from the first indication; and estimating the position of the electronic device based on at least one of the first and second positions, depending upon the first indication, the quality characteristic of the first match, the second indication and the quality characteristic of the second match,