1. An apparatus comprising: a map data storage device configured to store map data representing arrangement of map elements; a map update device configured to reflect a first map update of a first map element to a first version of the map data to produce a second version of the map data when the first map update occurs, the map update device configured to reflect a second map update of a second map element to the second version of the map data to produce a third version of the map data when the second map update occurs after the first map update; a determination device configured to determine whether the first map update and the second map update depend on each other by determining whether the first map element and the second map element have a common portion; and a data production device configured to produce map differential data from the first map update and the second map update when the determination device determines that the first map update and the second map update depend on each other.