1. A method of selecting an input activity of a computing system including a touch sensing surface, the method comprising: obtaining tracking information of contacts, the contacts corresponding to a plurality of hand parts contacting the touch sensing surface, the tracking information including first tracking information of a first hand part contact, the first tracking information including touchdown information of the touchdown of the first hand part contact, liftoff information of the liftoff of the first hand part contact, and lateral motion information of lateral motion of the first hand part contact between the touchdown and liftoff of the hand part first contact, and the tracking information including second tracking information of a second hand part contact, the second tracking information including touchdown information of the touchdown of the second hand part contact, liftoff information of the liftoff of the second hand part contact, and lateral motion information of lateral motion of the second hand part contact between the touchdown and liftoff of the second hand part contact; determining whether the first hand part contact based on the touchdown information of the first hand part contact; determining whether the second hand part contact is a resting contact based on the touchdown information of the second hand part contact; and periodically processing the tracking information, the processing including selection of input activities of the computing system, the selection of an input activity being based on the tracking information, wherein in accordance with a determination that the first hand part contact is not a resting contact and the second hand part contact is a resting contact, the periodic processing selects a first input activity based on at least one of the touchdown information, the lateral motion information, and the liftoff information of the first hand part contact and excludes the second tracking information corresponding to the second hand part contact from the selection of input activities; and in accordance with a determination that the first hand part contact is a resting contact and the second hand part contact is not a resting contact, the periodic processing selects a second input activity based on at least one of the touchdown information, the lateral motion information, and the liftoff information of the second hand part contact and excludes the first tracking information corresponding to the first hand part contact from the selection of input activities.