Abstract: A method of communicating electronic map data is disclosed, wherein map data is compiled as at least one cell comprising a plurality of vector data records and a plurality of feature data records to, for instance, the IHO S-57 standard. During the compilation, the respective bit lengths of a plurality of vector data values are reduced and both the bit-reduced vector data values and feature data values are entropy encoded. The compiled cell data, which may be an Electronic Navigational Chart, is then compressed, encrypted and digitally signed according to, for instance, the IHO S-63 standard. The encrypted and digitally signed cell data is eventually transmitted to a remote navigational system, which may be an Electronic Chart Display and Information System, over a network, for instance in a satellite telecommunication. A system embodying the method is also disclosed.