Anisotropy

Anisotropy (the opposite of isotropy) is the property of being directionally dependent. Something which is anisotropic, may appear different, or have different characteristics in different directions. An example is the polarising lens in a pair of Polaroid sunglasses, in which if you hold the lens in one direction, light streams through, whereas if you hold the lens in another direction, light is blocked.

Computer graphics
In the field of computer graphics, an anisotropic surface will change in appearance as it is rotated about its geometric normal, as is the case with velvet. Anisotropic scaling occurs when something is scaled by different amounts in different directions. An example is down-scaling a 64&times;64-pixel texture to cover a 12&times;34-pixel rectangle; this is anisotropic filtering.

An anisotropic filter, on the other hand, is a filter with increasingly smaller interstitial spaces in the direction of filtration so that the proximal regions filter out larger particles and distal regions increasingly remove smaller particles, resulting in greater flow-through and more efficient filtration.

Physics
Cosmologists use the term to describe the fluctuations in the background radiation left over after the big bang. The term refers to the difference in the temperature of the cosmic microwave background radiation with direction.

Physicists use the term to refer to some properties of plasmas. For example, a plasma may have a magnetic field orientated in a preferred direction, or show filamentation (such as that seen in lightning or a plasma globe) that is directional.

An anisotropic liquid is one which has the fluidity of a normal liquid, but, unlike water or chloroform, which contain no structural ordering of the molecules, they have an average structural order relative to each other along their molecular axis. Liquid crystals are examples of anisotropic liquids.

Some materials conduct heat in a way that is isotropic, that is independent of spatial orientation around the heat source. It is more common for heat conduction to be anisotropic, which implies that detailed geometric modeling of typically diverse materials being thermally managed is required. The materials used to transfer and reject heat from the heat source in electronics are often anisotropic.

Many crystals are anisotropic to light, and exhibit properties such as birefringence. Crystal optics describes light propagation in these media.

Geology
Geological formations where distinct layers of sedimentary material are disposited can exhibit electrical anisotropy. That is electrical conductivity in one direction e.g. parallel to a layer, is different to that in another e.g. perpendicular to a layer. This property is used in the gas and oil exploration industry to identify hydrocarbon-bearing sands in sequences of sand and shale. Sand bearing hydrocarbon assets have high resistivity (relatively low conductivity) whereas shales are much more conductive. Formation evaluation instruments measure this conductivity and resistivity and the results are used to help best site oil and gas wells.