When this change of datum occurred, we were instructed to change the lettering system for the 100 000-metre square identification grid on map sheets produced under the new datum. In the late eighties, Natural Resources Canada decided to use the North American Datum of 1983 (NAD83), instead of the North American Datum of 1927 (NAD27), as the official datum for our mapping activities. Reading from south to north, this lettering system is repeated every 2 000 000 metres. Starting at the equator and proceeding north, each row is lettered alphabetically, from A through V, with I and O omitted. Starting at the 180В° meridian and proceeding east along the equator, each 100 000-metre column is lettered alphabetically, from A through Z, with I and O omitted. Each 100 000-meter square is identified by a combination of two alphabetical letters. Our NTS sheets show the Military Grid Reference System, commonly known as the 100 000-metre square identification grid. Many National Topographic System (NTS) map sheets have been produced with the wrong two letter MGRS designators. This material updated from The Universal Transverse Mercator Grid, Department of Energy, Mines and Resources Canada, Surveys and Mapping Branch, Ottawa, В© 1969, The QueenвЂs Printer. Therefore the unique designation of the church if it were in the Ottawa area would be 18 T NT9293. The zone number is followed by a letter which gives the general area north or south of the equator in bands of 8 degrees. The zone, which is explained elsewhere, is one of the 60 strips of the projection. If, for some reason, a reference is required that is unique in the world, one must look in the margin of the map for the Grid Zone Designation. For most purposes this is sufficiently unambiguous. This reference is still not unique, but the same reference does not occur again for about 2,900 km (1,800 miles). Here the church would be in square NT99 and more precisely at point NT9293. Figure 3 shows a reference on a 1:250 000 map (where grid lines are usually identified by a single number). The identifying letters (two of them) are always given before the numbers. This is particularly important in the case of medium- and small-scale maps (1:250 000 and smaller), as unlettered references are ambiguous on a single map. Therefore a method has been devised to identify the 100,000-metre squares by letters which are printed in blue on the face of all NTS maps. The Military Grid Reference System is convenient, but unfortunately reference numbers repeat themselves every 100,000 metres (100 km or about 62 miles). Figure 3 is an illustration of reference numbers in blue which makes the unique referencing.

Miliary grid mapping