1. A signal space based navigation apparatus comprising: a processor; and a memory storing machine readable instructions that when executed by the processor cause the processor to: receive traces of wireless signal observations and corresponding pedestrian deadreckoning (PDR) traces between different ones of the wireless signal observations from a plurality of user devices; generate a plurality of wireless clusters based on the traces of wireless signal observations; generate a PDR displacement vector between at least two of the wireless clusters based on the at least two of the wireless clusters and a subset of the PDR traces corresponding to the at least two of the wireless clusters; and generate a sensing map based on the plurality of wireless clusters and a plurality of PDR displacement vectors including the PDR displacement vector.