Provided is a data transmission method, a communications network, a mobile receiving device and data processing methods for use in broadcast of geographic information to mobile devices. The invention overcomes the problem of lack of currency of static information distribution via CD-ROM, and the problem of the cost of lengthy connections to the Internet which is a requirement of some dynamic solutions. The geographic data which is relevant to a transmitter in the network is broadcast by the transmitter as a plurality of separate data elements which each relate to and include an identification of a specific map segment of a segmented map, such that the data elements can be transmitted independently of each other and the map segment identifier can be used by the receiving device to position the geographic information of each data element within the appropriate map segment. Each data element is retransmitted periodically such that gaps can be filled in and the map can be built up over time even if transmission failures occur during a transmission.