  Large patterns could exist on the microwave sky as a result of various
non-standard possibilities for the large-scale Universe -- rotation or shear,
non-trivial topology, and single topological defects are specific examples.
All-sky (or nearly all-sky) CMB data sets allow us, uniquely, to constrain such
exotica, and it is therefore worthwhile to explore a wide range of statistical
tests. We describe one such statistic here, which is based on determining
gradients and is useful for assessing the level of `preferred directionality'
or `stripiness' in the map. This method is more general than other techniques
for picking out specific patterns on the sky, and it also has the advantage of
being easily calculable for the mega-pixel maps which will soon be available.
For the purposes of illustration, we apply this statistic to the four-year COBE
DMR data. For future CMB maps we expect this to be a useful statistical test of
the large scale structure of the Universe. In principle, the same statistic
could also be applied to sky maps at other wavelengths, to CMB polarisation
maps, and to catalogues of discrete objects. It may also be useful as a means
of checking for residual directionality (e.g., from Galactic or ecliptic
signals) in maps.
