LAC zone(unofficial name)
A system for describing the zone of coverage of a lunar map in longitude and latitude. The entire lunar surface is first divided into 144 regions represented by an initial number in the range 1..144. Maps ("sheets") in the original Lunar Astronautical Chart series covered one of these zones, for example LAC-42. Next the primary numbered LAC zone is divided into 4 quadrants designated by one the letters A..D, which is placed after the initial number. Maps in the original Apollo Intermediate Chart series covered one of these sub-zones, for example AIC-42A. Finally, the AIC zones are each subdivided into four more quadrants designated by a trailing number in the range 1..4. Maps in the original Lunar Topographic Orthophotomap series covered one of these, for example, LTO-42A4.
In 1973, the IAU formally adopted the LAC zone system as a way to specify the location of lunar features (IAU Transactions XVB). In the system adopted, the 144 zones are referred to as "Regions" and each of the 16 LTO-sized tiles into which it is divided are called "Provinces". The IAU further proposed dividing each Province into 576 very small sub-Provinces designated by two additional letters: a capital letter indicating the position from west to east, and a lower-case letter indicating the position from south to north. Apparently it was intended that such names could be used to identify features that had not been assigned names. The full system with the two trailing letters to identify a feature's sub-Province was used on only a very few of maps prepared by the DMA.
In 1976, the IAU adopted and published an official IAU name for each of the 144 LAC "Regions" (IAU Transactions XVIB).
- The A..D sub-zones are quadrants arranged clockwise starting in the upper left of the full LAC zone. The final four numbered sub-quadrants are likewise arranged clockwise starting in the upper left of the A..D zone (see Figure 2 in IAU Transactions XVB).
- The unofficial term LAC zone has been introduced in the-Moon Wiki for indicating where features on the Moon's surface are located. The LAC zone given in the header to the Maps section of each feature page gives the LAC zone (as defined above) in which the feature's center coordinates (given in the title line) fall. It tells immediately which LAC, AIC and LTO map the feature would be plotted on.
- For maps covering successively larger areas, you simply ignore the final digits in the complete code. Conversely the full code can be examined to determine where the feature of interest falls on the larger map. In the full IAU system with the two trailing letters, a very small region is designated and its position can be determined by the coding. Why this was considered superior to giving the longitude and latitude of the feature is unclear; although military organizations have found a similar system useful for specifying small regions on the Earth.
- Maps in the Lunar Topophotomap and Lunar Photomap (Site Traverses) series cover still smaller areas, but do not correspond to the IAU sub-provinces. Their names use the full LAC zone designator with still more letters and numbers at the end, for example Topophotomap-42A4S1(10). "S1" presumably stands for "Special 1". The final number in parenthesis is the scale, or magnification, of the image relative to the real moon, in this case 1:10,000. - Jim Mosher