1. A method of setting links suitable for map matching, comprising: in a map matching system comprised representing a road network with at least a first road and a second road, the second road parallel to the first road, the first road having a first width different from a second width of the second road, a separating zone existing between the first and second roads, upon setting a first link on the first road, giving said first link a width in accordance with the first width of said first road and an error in a current location of the first link as acquired by on-board equipment; upon setting a second link on the second road, giving a width to the second link in accordance with the second width of the second road and an error in a current location of the second link as acquired by the on-board equipment; extracting an overlapping portion between the first and second links; calculating a shifting direction and a shifting distance so that no overlap appears between the first and second links; and shifting one of the first and second links based on the calculated shifting direction and calculated shifting distance so that there is no overlap between the first and second links.