The arrange design choice covers all aspects of the use of spatial channels for visual encoding. It is the most crucial visual encoding choice because the use of space dominates the user's mental model of the dataset. The three highest ranked effectiveness channels for quantitative and ordered attributes are all related to spatial position: planar position against a common scale, planar position along an unaligned scale, and length. The unique values for a categorical or ordered attribute are called levels, to avoid the confusion of overloading the term value. Using space to express quantitative attributes is a straightforward use of the spatial position channel to visually encode data. The attribute is mapped to spatial position along an axis. In the simple case of encoding a single value attribute, each item is encoded with a mark at some position along the axis. Additional attributes might also be encoded on the same mark with other non-spatial channels such as color and size.