1. An apparatus, comprising: at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform operations comprising: acquiring indoor non-labeled Earth's magnetic field, EMF, data sets representing at least one of magnitude and direction of the EMF in a building from a plurality of mobile devices, wherein routes corresponding to the non-labeled EMF data sets in the building are unknown; acquiring motion data sets from the plurality of mobile devices; estimating route models of the traveled routes based on the motion data sets; generating EMF fingerprints for the traveled routes by associating the acquired EMF data sets with the route models; determining locations of the routes with respect to each other based on at least one of the following: the EMF fingerprints and the route models; and clustering the plurality of the mobile devices geographically based on the generated EMF fingerprints.