17. A system for inferring location context categories for a set of mobile users having at least two members, comprising: a computer server, having a processor and a memory, configured to: for each mobile user in the set, obtain at least one location context category therefor from publically available information responsive to uncertain mobile device location data; and apply multi-user collaborative machine learning with an objective function to the at least one location context category for each mobile user in the set to infer a single refined location context category for each mobile user in the set to form a matrix.
17. A system for inferring location context categories for a set of mobile users having at least two members, comprising: a computer server, having a processor and a memory, configured to: for each mobile user in the set, obtain at least one location context category therefor from publically available information responsive to uncertain mobile device location data; and apply multi-user collaborative machine learning with an objective function to the at least one location context category for each mobile user in the set to infer a single refined location context category for each mobile user in the set to form a matrix. 18. The system of claim 17 , wherein the computer server is implemented using a cloud computing configuration.