Note: The count of links refers to divided highways; both directions are included in one link. (As of March 31, 2013)
Initially, the DRM Database was created based on the 1:25,000 topographic maps issued by the Geospatial Information Authority of Japan(GSI). Since then, the database has been updated every year based on new topographic maps as well as information from the Ministry of Land, Infrastructure and Transport, prefecture governments, municipalities, expressway companies, and road-related public corporations.
Since 2010, the database has been updated based on the 1:2,500 Fundamental Geospatial Data issued by the GSI. The database consists of 4748 secondary grid cell map data in 2013.
The database consists of 4748 secondary grid cell map data in 2013.