  This paper describes a programme to map large-scale cosmic structures on the
largest possible scales by using the Five hundred metre Aperture Spherical
Telescope (FAST) to make a 21 cm (red-shifted) intensity map of the sky for the
range $0.5 < z < 2.5$. The goal is to map to the angular and spectral
resolution of FAST a large swath of the sky by simple drift scans with a
transverse set of beams. This approach would be complementary to galaxy surveys
and could be completed before the Square Kilometre Array (SKA) could begin a
more detailed and precise effort. The science would be to measure the
large-scale structure on the size of the baryon acoustic oscillations and
larger scale, and the results would be complementary to its contemporary
observations and significant. The survey would be uniquely sensitive to the
potential very large-scale features from inflation at the Grand Unified Theory
(GUT) scale and complementary to observations of the cosmic microwave
background.
