  We present the $^{13}$CO/C$^{18}$O (J=3-2) Heterodyne Inner Milky Way Plane
Survey (CHIMPS) which has been carried out using the Heterodyne Array Receiver
Program on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. The
high-resolution spectral survey currently covers |b| < 0.5 deg and 28 < l < 46
deg, with an angular resolution of 15 arcsec in 0.5 km/s velocity channels. The
spectra have a median rms of $\sim$ 0.6 K at this resolution, and for optically
thin gas at an excitation temperature of 10 K, this sensitivity corresponds to
column densities of $N_{\mathrm{H}_{2}} \sim 3 \times 10^{20}\,$cm$^{-2}$ and
$N_{\mathrm{H}_{2}} \sim 4 \times 10^{21}\,$cm$^{-2}$ for $^{13}$CO and
C$^{18}$O, respectively. The molecular gas that CHIMPS traces is at higher
column densities and is also more optically thin than in other publicly
available CO surveys due to its rarer isotopologues, and thus more
representative of the three-dimensional structure of the clouds. The critical
density of the J=3-2 transition of CO is $\gtrsim 10^{4}$ cm$^{-3}$ at
temperatures of $\leq 20$ K, and so the higher density gas associated with star
formation is well traced. These data complement other existing Galactic plane
surveys, especially the JCMT Galactic Plane Survey which has similar spatial
resolution and column density sensitivity, and the Herschel infrared Galactic
Plane Survey. In this paper, we discuss the observations, data reduction and
characteristics of the survey, presenting integrated emission maps for the
region covered. Position-velocity diagrams allow comparison with Galactic
structure models of the Milky Way, and while we find good agreement with a
particular four arm model, there are some significant deviations.
