An apparatus (100, 200) comprising: at least one memory (120, 220); and at least one processor (110, 210), wherein the memory comprises computer code stored thereon, the code being configured to, when run on the processor, cause the apparatus to perform at least: - receiving partial Global Navigation Satellite System, GNSS, data from one or more respective GNSS satellites relating to the geographical location of a first portable electronic device, wherein the received partial GNSS data is insufficient, by being corrupt, for determining the geographical location of the first portable electronic device; - communicating with one or more further portable electronic devices in proximity to the first portable electronic device to access corresponding partial GNSS data relating to the geographical location of the respective further portable electronic devices, the partial GNSS data of the one or more respective further portable electronic devices being corrupt; - measuring a synchronisation error between the first and respective further portable electronic devices based on a comparison between the respective further and first portable electronic device partial GNSS data to allow for synchronisation of the respective further and first portable electronic device partial GNSS data, wherein the synchronisation error is measured by identifying a time difference between one or more common timestamp peaks of the partial GNSS data from the respective further and first portable electronic devices; and - using the measured synchronisation error and the accessed partial GNSS data of the further portable electronic devices to supplement the received partial GNSS data of the first portable electronic device to thereby determine the geographical location of the first portable electronic device. at least one memory (120, 220); and at least one processor (110, 210), wherein the memory comprises computer code stored thereon, the code being configured to, when run on the processor, cause the apparatus to perform at least: - receiving partial Global Navigation Satellite System, GNSS, data from one or more respective GNSS satellites relating to the geographical location of a first portable electronic device, wherein the received partial GNSS data is insufficient, by being corrupt, for determining the geographical location of the first portable electronic device; - communicating with one or more further portable electronic devices in proximity to the first portable electronic device to access corresponding partial GNSS data relating to the geographical location of the respective further portable electronic devices, the partial GNSS data of the one or more respective further portable electronic devices being corrupt; - measuring a synchronisation error between the first and respective further portable electronic devices based on a comparison between the respective further and first portable electronic device partial GNSS data to allow for synchronisation of the respective further and first portable electronic device partial GNSS data, wherein the synchronisation error is measured by identifying a time difference between one or more common timestamp peaks of the partial GNSS data from the respective further and first portable electronic devices; and - using the measured synchronisation error and the accessed partial GNSS data of the further portable electronic devices to supplement the received partial GNSS data of the first portable electronic device to thereby determine the geographical location of the first portable electronic device. - receiving partial Global Navigation Satellite System, GNSS, data from one or more respective GNSS satellites relating to the geographical location of a first portable electronic device, wherein the received partial GNSS data is insufficient, by being corrupt, for determining the geographical location of the first portable electronic device; - communicating with one or more further portable electronic devices in proximity to the first portable electronic device to access corresponding partial GNSS data relating to the geographical location of the respective further portable electronic devices, the partial GNSS data of the one or more respective further portable electronic devices being corrupt; - measuring a synchronisation error between the first and respective further portable electronic devices based on a comparison between the respective further and first portable electronic device partial GNSS data to allow for synchronisation of the respective further and first portable electronic device partial GNSS data, wherein the synchronisation error is measured by identifying a time difference between one or more common timestamp peaks of the partial GNSS data from the respective further and first portable electronic devices; and - using the measured synchronisation error and the accessed partial GNSS data of the further portable electronic devices to supplement the received partial GNSS data of the first portable electronic device to thereby determine the geographical location of the first portable electronic device.