1. A method comprising, at a mobile device: transmitting one or more indicators of a location of the mobile device to a server; receiving from said server parameters representing an inference model based, at least in part, on the one or more indicators of said location; determining that said mobile device is located in or approaching a particular region of a plurality of candidate regions based, at least in part, on application of one or more observations obtained by said mobile device to said parameters representing said inference model, wherein the plurality of candidate regions comprise at least one indoor region and at least one outdoor region; transmitting a request message to said server indicating that said mobile device is located in or approaching the particular region; and receiving from said server positioning assistance data determined based, at least in part, on said request message.