A method performed by a network node in a cellular communications network, the method comprising: allocating to a user equipment device a mobility area, wherein the user equipment device is not required to inform the network of its location while it remains in the mobility area, wherein the mobility area is formed by a plurality of tracking areas, and wherein each tracking area has a respective identifier comprising a plurality of bits; and the method characterised by: providing 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 and wherein the information identifying the plurality of tracking areas forming the mobility area allocated to the user equipment device is either: a truncated identifier, wherein the bits of said truncated identifier match the most significant bits of a plurality of identifiers of respective tracking areas; or a mask, indicating a subset of the bits of each identifier, wherein a plurality of identifiers of respective tracking areas are identical when considering only said subset of the bits; or comprises applying a hash function to the respective identifiers of the plurality of tracking areas forming the mobility area allocated to the user equipment device; and providing said information to the user equipment device identifying the plurality of tracking areas forming the mobility area, wherein said information identifying the plurality of tracking areas forming the mobility area comprises an output of the hash function; or comprises information identifying a plurality of tracking areas; and a bitmap, wherein each bit of the bitmap indicates whether a respective one of said tracking areas does or does not form part of the mobility area allocated to the user equipment device. allocating to a user equipment device a mobility area, wherein the user equipment device is not required to inform the network of its location while it remains in the mobility area, wherein the mobility area is formed by a plurality of tracking areas, and wherein each tracking area has a respective identifier comprising a plurality of bits; and the method characterised by: providing 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 and wherein the information identifying the plurality of tracking areas forming the mobility area allocated to the user equipment device is either: a truncated identifier, wherein the bits of said truncated identifier match the most significant bits of a plurality of identifiers of respective tracking areas; or a mask, indicating a subset of the bits of each identifier, wherein a plurality of identifiers of respective tracking areas are identical when considering only said subset of the bits; or comprises applying a hash function to the respective identifiers of the plurality of tracking areas forming the mobility area allocated to the user equipment device; and providing said information to the user equipment device identifying the plurality of tracking areas forming the mobility area, wherein said information identifying the plurality of tracking areas forming the mobility area comprises an output of the hash function; or comprises information identifying a plurality of tracking areas; and a bitmap, wherein each bit of the bitmap indicates whether a respective one of said tracking areas does or does not form part of the mobility area allocated to the user equipment device. a truncated identifier, wherein the bits of said truncated identifier match the most significant bits of a plurality of identifiers of respective tracking areas; or a mask, indicating a subset of the bits of each identifier, wherein a plurality of identifiers of respective tracking areas are identical when considering only said subset of the bits; or comprises applying a hash function to the respective identifiers of the plurality of tracking areas forming the mobility area allocated to the user equipment device; and providing said information to the user equipment device identifying the plurality of tracking areas forming the mobility area, wherein said information identifying the plurality of tracking areas forming the mobility area comprises an output of the hash function; or comprises information identifying a plurality of tracking areas; and a bitmap, wherein each bit of the bitmap indicates whether a respective one of said tracking areas does or does not form part of the mobility area allocated to the user equipment device.