This is a description of "How astronomers use multi-dimensional data" diagram, image dimensions_fig-690.jpg, from the home page.
The diagram consist of 5 columns and 3 rows. Each column shows the types of the quantities measured by astronomers (middle row), the dimensionality of each measured quantity (top row) and the information which stronomers can derive using this measured data (bottom row).
The dimensionality runs from 2D (the first, leftmost, column), through 3D, 5D and 6D to 12+D (the last column, furthest to the right). The dimensionalities, their corresponding measured quantities and derived information are listed below. Key: Each sentence gives: Dimensionality; corresponding measured quantities; derived information.
2D; position; What is there? Where is it?
3D; parallax; distance.
5D; proper motions; Transverse velocities.
6D; Spectrum & Doppler shift; Radial velocity + chemistry.
12+D; Stellar properties; Ages, histories, astrophysics.