1. A method comprising: collecting from each of first multiple access points in a network of access points a set of measurements, each said set of measurements being made at a respective one of the first multiple access points as a result of the respective one of the first multiple access points receiving signals transmitted by other ones of the first multiple access points, wherein the first multiple access points are configured for use in positioning a device that communicates with but is not part of the network of access points; processing the collected sets of measurements to classify changes that have occurred indicating an inconsistency between configuration of the network of access points and stored configuration information, wherein classification comprises identifying a change as consequent on one of: access point position change, access point orientation change, access point transmission power change, access point addition or access point removal; and performing an action that is conditional upon how a change is classified.