The ODI will allow high-precision parallax (0.6 mas per star) and proper-motion (0.5 mas/yr per star in 2-3 years) measurements to I <= 22. There are several topics of Galactic structure that can be addressed with the Yale ODI survey.
Sagittarius dwarf galaxy (Sgr) has a polar orbit, with the orbital plane nearly coincident with the X-Z Galactic plane. The trailing tail of Sgr that arches just beneath the Solar neighborhood is spatially best defined due to the geometry of the orbit. Thus proper motions along Galactic longitude in the trailing tail are mainly due to the reflex Solar motion and offer a direct measurement of rotation of the Local Standard of Rest.
By measuring accurate proper motions along a contiguous ~5-degree portion of this stream (from region one of the ODI survey), the Local Standard of Rest velocity and the flattening of the Galactic potential can be well constrained. In addition, the existence (or not) of multiple Sgr streams (in proper-motion space) in the same region can be probed and used to constrain the flattening of the potential (see Majewksi et al. 2006, Law et al. 2005).
The structure now known as the Monoceros stream/ring (Mon) that encircles the Milky Way at a distance of ~20 kpc still has a controversial origin: a disrupted satellite system or a perturbation of the Galactic disk. If interpreted as a disrupted satelite, its main core has yet to be found, and models constrained by data at different locations on the sky differ in the predicted orbits (e.g. Penarrubia et al. 2005 versus Grillmair et al. 2008). Equally difficult it is to explain Mon as a perturbation of the disk, over such a large extent around the Galaxy. Region two of the ODI survey samples a very complex part of the Mon (on or near Grillmair et al. 2008) where accurate proper motions over a substantial area will help better understand the velocity structure of this stream and its likely origin.
With an estimated parallax error of 0.6 mas for a single star for I <= 22, the stellar density within 150 pc from the Sun will be determined to 1.5%, as well as probe the faint end of the luminosity function in the Solar neighborhood to an M_V ~ 20 (the main-sequence minimum mass range corresponds to an M_V = 17 to 19).