1. A file creation method, comprising: creating file content at a particular location and time using a portable device; obtaining data from wireless communication devices detectable by the portable device at the particular location and time thereby to obtain a set of data, the set of data identifying or enabling identification of the wireless communication devices; associating the set of data and time with the file content to enable subsequent analysis to determine the particular location using a time-dependent database wherein the location is determined based on reference data for approximately the time associated with the file content.