One application of the invention is in rental cars equipped with a vehicle navigation system.

A kiosk located at the car rental agency may be employed to feed the information into a smart card which the customer then inserts into the vehicle navigation system of rental car.

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.

The present invention relates to the field of data communications, and in particular to the provision of information to a portable or other mobile device such as a mobile telephone, a lap-top or palm-sized data processing device, a data processing system integrated within a vehicle, or any other mobile receiver device.

Currently, solutions for providing information for route planning and associated tourist guides are delivered as static databases to work with an application (e.g. Microsoft AutoMap), usually on a CD-ROM.

The main disadvantages of such solutions are that the finite space of the storage medium restricts the scale of the information and, being static, the information is inherently dated.

The storage capacity issue is being worked on by Matsushita Communication Industrial Co., Ltd. and others, but this and the lack of currency of information remain significant issues especially for supplementary data such as hotel guides and services information which is associated with a map.

Alternative solutions which provide a dynamic solution are typically based on the World Wide Web Internet service.

Since the information held on a Web server computer can be updated whenever appropriate, it is possible to ensure that the information accessed by end users via their Web Browsers is current.

However, such solutions require the user to either download the pertinent information to their laptop or other portable device before leaving on a journey, or having to browse the information over an expensive dialup service to the Internet during the journey.

UK patent application GB-A-2195868 proposed an alternative solution in which a plurality of transmitters, located in different regions and broadcasting on different frequencies, each broadcast map information relating to their respective regions.

Portable receivers are able to receive broadcasts from any of the transmitters and are able to display a map generated from the broadcast information.

Significant problems with the solution suggested in GB-A-2195868, and with many other dynamic solutions, include the problems inherent in currently available wireless communications of potential failures to receive a complete transmission.

Such failures may occur for example because the mobile device is temporarily shielded during receipt of a transmission, such as when a user drives into a tunnel, or because the mobile device moves out of the range of the transmitter during receipt of a transmission.

Also, the mobile device may be switched off during receipt of a transmission.

These problems are emphasized by the typically large amount of geographic information which has to be successfully transmitted in order to give reasonable map detail, since this is relevant to both the likelihood of a failure before transfer is complete and the time required for retransmission.

Matsushita Electric Industrial Co., Ltd. has announced development of a map processing technology which automatically processes maps into a simplified form before they are transmitted to a PDA.

The simplified maps have a reduced data size compared with the original maps and so can be transmitted more quickly as well as being easier to read on PDA screens.

Although such a solution increases the likelihood of map data being transferred before a communication failure occurs and reduces the transfer time, the Matsushita map reduction solution does not solve the problems of communication failures which occur during a data transfer.

Additional disclosures of map broadcasting solutions which suffer from the above-described problems of communication failures can be found in Japanese patent application JP6229768 (which describes FM broadcasting of map data and uses a position detector, superimposing the vehicle position on a map image generated from the broadcast data) and JP8201085 (which describes a navigation system implementing a method for reducing the requirement for switching of FM broadcasting stations by selecting an optimal FM broadcasting station for a recommended route to a destination).

Additionally, French patent application FR2742565 discloses data being broadcast by digital radio and then being filtered on receipt to extract information relevant to the current zone in which a vehicle is located.

The present invention provides methods and apparatus for broadcast of geographic information to mobile devices, in which the information is organised for transmission as a plurality of data elements which each relate to and include an identification of a particular segment or region of a map.

Positions on the map can be defined with reference to segments or regions.

For the purposes of data transmission, the data elements are treated as independent of each other.

"Geographic information" in this context includes map and route information and any information which has a geographic relevance such as weather, traffic and local services information.

The data elements each include a map reference which is sufficient to uniquely locate them in a map.

This independent self-identification of map location within each data element ensures that the data elements can be transmitted and received independently of each other and received elements can then be processed at the mobile device to build up a meaningful representation of received geographic information even if one or more of the transmitted data elements is not received.