considered valid if any part of the square which they denote lies within the latitude zone specified by the third letter of the string. Polar regions In the polar regions, a different convention is used. South of 80°S, UPS South (Universal Polar Stereographic) is used instead of a UTM projection. The west half-circle forms a grid zone with designation A; the east half-circle forms one with designation B; see figure 3. North of 84°N, UPS North is used, and the west half-circle is Y, the east one is Z; see figure 4. Since the letters A, B, Y, and Z are not used for any latitude bands of UTM, their presence in an MGRS coordinate, with the omission of a zone number, indicates that the coordinates are in the UPS system. The lettering scheme for 100,000 m squares is slightly different in the polar regions. The column letters use a more restricted alphabet, going from A to Z but omitting D, E, I, M, N, O, V, W; the columns are arranged so that the rightmost column in grid zone A and Y has column letter Z, and the next column in grid zone B or Z starts over with column letter A. The row letters go from A to Z, omitting I and O. The restricted column alphabet for UPS ensures that no UPS square will be adjacent to a UTM square with the same identification. In the polar regions, there is only one version of the lettering scheme. See also There are other geographic naming systems of this alphanumeric kind: Global Area Reference System (GARS) has been adopted by the National Geospatial-Intelligence Agency for use across the Department of Defense for certain applications. GARS defines areas of 30x30, 15x15, and no smaller than 5x5 minutes of latitude and longitude. Ordnance Survey National Grid is another Transverse Mercator system designed for locations in the British Isles Irish Transverse Mercator has replaced the Irish grid reference system United States National Grid (USNG), developed by the Federal Geographic Data Committee. World Geographic Reference System (GEOREF) has been used for air navigation, but is rarely seen today. Maidenhead Locator System is used by amateur radio operators. Natural Area Code References External links A list of coordinate systems – by Prof. Peter H. Dana at the Univ. of Colorado Grids and Reference Systems, by NGA. Army Study Guide: Locate a point using the