A middle ultraviolet imager (235--263 nm) on the Midcourse Space Experiment (MSX) has obtained the first large-scale, two-dimensional maps of polar mesospheric clouds (PMCs). The lower parts of individual images, which lie below the ozone horizon, are mapped onto an ellipsoidal shell at 83 km altitude and then combined to establish the transpolar PMC field in two spatial dimensions across the entire polar region. At all latitudes where they appear, the PMCs clearly evidence a patchy structure as opposed to a uniform layer. Among the interesting features of these cloud patches are zonal alignments, arcs, and repetitive structures characteristic of waves. Whether random or repetitive, the cloud structures exhibit scales ranging from several hundred kilometers down to tens of kilometers.