  Disk winds are thought to play a critical role in the evolution and dispersal
of protoplanetary disks. A primary diagnostic of this physics is emission from
the wind, especially in the low-velocity component of the [O I] $\lambda6300$
line. However, the interpretation of the line is usually based on spectroscopy
alone, which leads to confusion between magnetohydrodynamic winds and
photoevaporative winds. Here we report that in high-resolution spectral mapping
of TW Hya by the multi-unit spectroscopic explorer at the Very Large Telescope,
80% of the [O I] emission is confined to within 1 AU radially from the star. A
generic model of a magnetothermal wind produces [O I] emission at the base of
the wind that broadly matches the flux and the observed spatial and spectral
profiles. The emission at large radii is much fainter that predicted from
models of photoevaporation, perhaps because the magnetothermal wind partially
shields the outer disk from energetic radiation from the central star. This
result calls into question the previously assessed importance of
photoevaporation in disk dispersal predicted by models.
