A network node in a cellular communications network allocates a mobility area to a user equipment device, such that the user equipment device is not required to inform the network of its location while it remains in the mobility area. The mobility area comprises a plurality of tracking areas, and each tracking area has a respective identifier comprising a plurality of bits. The network node provides information to the user equipment device identifying the plurality of tracking areas forming the mobility area allocated to the user equipment device, wherein said information identifying the plurality of tracking areas forming the mobility area comprises fewer bits of information than the total number of bits in the respective identifiers of the plurality of tracking areas.