  It is widely believed that T Tauri winds are driven magnetocentrifugally from
accretion disks close to the central stars. The exact launching conditions are
uncertain. We show that a general relation exists between the poloidal and
toroidal velocity components of a magnetocentrifugal wind at large distances
and the rotation rate of the launching surface, independent of the uncertain
launching conditions. We discuss the physical basis of this relation and verify
it using a set of numerically-determined large-scale wind solutions. Both
velocity components are in principle measurable from spatially resolved
spectra, as has been done for the extended low-velocity component (LVC) of the
DG Tau wind by Bacciotti et al. For this particular source, we infer that the
spatially resolved LVC originates from a region on the disk extending from
$\sim 0.3$ to $\sim 4.0\AU$ from the star, which is consistent with, and a
refinement over, the previous rough estimate of Bacciotti et al.
