Starting at the 180th meridian and progressing
eastward by the compass, the earth’s surface is divided
into a succession of north-south zones, each
extending for 6 degrees of longitude. These zones are
numbered from 1 through 60. Between latitude 80°S
and 84°N, each zone is divided into a succession of
east-west rows, each containing 8 degrees of latitude,
with the exception of the northernmost row, which
contains 12 degrees of latitude. Rows are designated
by the letters C through X, with the letters I and O
omitted. The lettering system begins at the
southernmost row and proceeds north. For a particular
zone-row area, the designation consists of first, the
zone number and next, the row letter, such as 16S,
which means row S in zone 16.
The polar regions (that is, the areas above 84°N
and below 80°S) have only two zones in each area.
These lie on either side of the 0-degrees and 180-
degrees meridian. In the North Polar region, the half
of the region that contains the west longitudes is zone
Y; that containing the east longitudes is zone Z. No
numbers are used with these designations. Similarly,
in the South Polar region, the half containing the west
longitudes is zone A; that containing the east
longitudes, zone B.
In the UTM Military Grid System, a particular
point on the earth is further identified by the 100,000-
meter square in which it happens to lie. Each of the
6-degree longitude by 8-degree latitude zone-row
areas in the system is subdivided into squares
measuring 100,000 meters on each side. Each north-
south column of 100,000-meter squares is identified
by letter as follows. Beginning at the 180th meridian
and proceeding eastward, you will find six columns of
full squares in each 6-degree zone. Besides the full
columns, usually partial columns also run along the
zone meridians. The partial columns and full columns
in the first three zones are lettered from A through Z,
again with the letters I and O omitted. In the next time
zones, the lettering systems begins over again.
Observe, for example, figure 9-14, view B. This
figure shows the zone-row areas in 1N, 2N, and 3N,
and 1P, 2P, and 3P. The zone meridians shown are
180°W, 174°W, 168°W, and 162°W; the zone-row
parallels shown are the equator (0° latitude), 8°N, and
16°N. The first 100,000-meter-square column to the
east of 180 degrees is the partial column A. Next
comes six full columns: B, C, D, E, F, and G. Then
comes partial column H, to the west of the zone
meridian 174°W. The first column to the east of zone
meridian 174°W is partial column J; then comes the
full-size columns K, L, M, N, P, and Q, followed by
partial column R. To the east of zone meridian 168°W,
the first column is partial column S; then comes the
six full columns T, U, V, W, X, and Y, and the partial
column Z to the west of zone meridian 162°W.
The east-west rows of 100,000-meter squares are
designated by the letters A through V, again with I and
O omitted. For columns in the odd-numbered zones,
the first row of squares north of the equator has the
letter designation A; for columns in the even-
numbered zones, the first row of squares north of the
equator has the letter designation F. Rows above and
below this row are designated alphabetically. The first
row south of the equator in the odd-numbered zones,
for example, has the letter designation V, while the
first row south of the equator in the even-numbered
zones has the letter designation E.
The complete designation for a particular
100,000-meter square consists of the number-letter,
zone-row designation plus the two-letter, 100,000-
meter-square designation. For example, the
designation 1NBA means the first full square east of
the 180th meridian and north of the equator (square
BA) in zone-row 1N, as shown in figure 9-14, view B.
If you know the latitude and longitude of a certain
point on the earth, you can determine the designation
of the 100,000-meter square in which the point lies.
Take Fort Knox, Kentucky, for example, which lies
approximately at latitude longitude
You will find this latitude and longitude in
figure 9-15. The point lies in column 16, row S, and
100,000-meter square ES; therefore, the 100,000-
meter-square designation for Fort Knox, Kentucky, is
16SES.
The location of a particular point within a
100,000-meter square is given by naming the grid
coordinates of the 100-meter square (or, for more
precise location, of the 10-meter square) in which the
point lies. Within each zone the point of origin for
measuring these coordinates is the point of
intersection between the zone central meridian and
the equator. A false easting of 500,000 meters, instead
of a value of O meters, is assigned to the central
meridian to avoid the use of west or negative east-west
coordinates. For points in the earth’s Southern
Hemisphere, the equator is assigned a false northing
of 10,000,000 meters to avoid the use of south or
negative north-south coordinates, and northing values
decrease from the equator toward the South Pole. For
points in the Northern Hemisphere, the equator has a
coordinate value of 0 meters, and northing values
increase toward the North Pole.
This procedure results in very large coordinate
values when the coordinates are referenced to the
9-14
