Map display device and map display system

A map display device (10) comprises: a processing unit (21) to define a coordinate system on a map containing a component polygon indicating elements of an urban map; a processing unit (22) to set coordinates located inside the component polygon as interior coordinates and to set coordinates located outside of the component polygon as exterior coordinates; a processing unit (23) to calculate the moving average value for each coordinate in the coordinate system; a processing unit (24) to reset, from the exterior coordinates, coordinates that have a moving average value greater than a prescribed value as interior coordinates; a processing unit (26) to set, as an urban polygon, a polygon that follows the periphery of a region comprising a collection of set or reset interior coordinates; and a processing unit (27) to set the urban map to be displayable when the current location is within the urban polygon.