1. A navigation method for displaying a map image on a screen, comprising the following steps of: displaying a map image on the screen and specifying a center point on the map image; and shrinking the map image coaxially relative to the center point based on a non-linear &lsqb;or linear&rsqb; function in such a way that shrink rates of the map images at the same coaxial distance from the center point are the same throughout the screen; whereby displaying images that have been outside of the screen within the screen.