In RF based indoor positioning systems, RF map is constructed by collecting Received Signal Strength (RSS) values from access points at predetermined reference points in the working area. RF map is calibrated in order to compare with the measurements obtained using heterogeneous mobile devices and is updated to adapt to the environment dynamics before positioning. These processes, which are defined as RF map calibration and update respectively in the literature, play important roles in positioning accuracy. In this paper, a survey is presented by reviewing the workson RF map construction, calibration and update.