Method for compressing navigation map data

The present invention relates to a method for generating compressed navigation map database from uncompressed navigation map data, the uncompressed navigation map data containing different building blocks of navigation data, each building block addressing a specific functional aspect of the navigation data, each block containing strings of data, the method comprising the steps of: - determining, for each block of the uncompressed navigation map data, most frequent substrings of the block (21), - storing, for each block, the determined most frequent substrings of the block in a seed block (22), - replacing, for each block, in the strings the determined most frequent substrings stored in the seed block by a reference to the seed block thereby generating a compressed block for each block (23), - storing, for each block, the compressed block and the seed block in order to generate the compressed navigation map database (24).