Larger mowers are usually ganged (equipped with a number or gang of similar cutting units), so they can adapt individually to ground contours. They may be powered and drawn by a tractor or draft animals. The cutting units can be mounted underneath the tractor between the front and rear wheels, mounted on the back with a three-point hitch or pulled behind the tractor as a trailer. There are also dedicated self-propelled cutting machines, which often have the mower units mounted at the front and sides for easy visibility by the driver. Boom or side-arm mowers are mounted on long hydraulic arms, similar to a backhoe arm, which allows the tractor to mow steep banks or around objects while remaining on a safer surface.