## The Frame Model

The best way to think about a FrameFrame is like the frame that you would plot around a graph. In two dimensions, you would have an “99#99” and a “100#100” axis, a title on the graph and labels on the axes, together with an indication of the physical units being plotted. The values marked along each axis would be formatted in a human-readable way. The frame around a graph therefore defines a coordinate space within which you can locate points, draw lines, calculate distances, etc.

An AST Frame works in much the same way, embodying all of these concepts and a few more. It also allows any number of axes, which means that a Frame can represent coordinate systems with any number of dimensions. You specify how many when you create it.

Remember that the basic Frame we are considering here is completely general. It knows nothing of celestial coordinates, for example, and all its axes are equivalent. It can be adapted to describe any general purpose Cartesian coordinate system by setting its attributes, such as its TitleTitle and axis Labels, etc. to appropriate values.