Currently available isentropic maps of potential vorticity (IPV maps) are of low resolution. In this note, we examine the possibility of using 6.7 micron satellite-derived water vapour measurements to obtain higher resolution information about IPV distributions. While attempts to relate the two data sets analytically have so far proved unsuccessful, a qualitative comparison shows very similar features in both. Our results suggest that, over limited areas, it may be possible to use 6.7 micron brightness temperatures to obtain approximate contours for water vapour mixing ratio on a particular isentropic surface in the upper troposphere. For ares free of high clouds, these contours are expected to parallel the IPV contours on this surface. In a case study, the resulting map exhibits dramatically increased horizontal resolution compared with present IPV maps, detailing an intriguing upper-tropospheric feature at sub-synoptic scales.