This document discusses keys for visual image interpretation including tone, texture, pattern, size, shape, shadow, association, and site. Tone refers to the brightness or color of objects. Texture is the frequency of tonal variations. Pattern is the spatial arrangement of objects. Size is important for assessing objects relative to the scene and resolution. Shape is the most important factor for recognition. Shadow can help with interpretation but also cause difficulties. Association refers to how features relate to each other. Site refers to topographic location which is important when other elements don't clearly identify objects.