Road link string conversion method, road information providing device and road information providing system

A road link string conversion method for converting first road link string data included in first map data into second road link string data included in second map data: deciding whether or not first coordinates-of-position strings corresponding to the first road link string data correspond to the second road link string data; constructing a second coordinates-of-position string by combining together the first coordinates-of-position strings decided as not corresponding to the second road link string data; establishing correspondence between the second coordinates-of-position string and the second road link string data; and converting the first road link string data including the first coordinates-of-position strings decided as not corresponding to the second road link string data, to the second road link string data to which the second coordinates-of-position string corresponds.