This paper proposes a new representation, called a sky-ground representation, for describing scenes of environment at a local place. A sky-ground representation is a spherical image with full field of view, combined with a vertical reference which is determined by sensing the direction of gravity. The scene of environment at a local place is observed by a spherical image sensor. The acquired spherical image is divided into two parts, sky part and ground part, along the horizon according to their positions, above or below the horizon. The horizon is determined by sensing the gravity from an acceleration sensor.