A non-transitory computer-readable medium having embodied thereon a program, which when executed by a computer causes the computer to execute a method, the method comprising:
- updating information regarding an obstacle region and information regarding an empty region, an obstacle existing in space where a mobile body moves in the obstacle region, the obstacle not existing in the empty region;
- erasing information regarding the obstacle region or the empty region in a region unobservable from the mobile body after a predetermined period of time has elapsed since the information regarding the obstacle region or the empty region was obtained;
- and
- updating the obstacle region, and updating the empty region on a basis of different periods of elapsed time.