# DMA TECHNICAL MANUAL 8358.1

Datums, Ellipsoids, Grids, and Grid Reference Systems

TM 8358.1 Sections 4-1 through 6-6

## CHAPTER 4 THE NONSTANDARD SYSTEMS IN CURRENT USE

### 4-1 NONSTANDARD GRIDS ON MAPS AND CHARTS.

4-1.1 Nonstandard Grids.

4-1.1.1 There is no regular or uniform global plan for the various grids which make up the nonstandard grid systems. Some were originally developed by the native country and later conveniently adopted by the British and U.S. with or without modifications. Others are of British or French origin. The systems were devised or adopted at different times and, except in certain geographic areas, do not have a direct relationship with one another. Primary considerations in the selection of a grid were the projection, ellipsoid, origin, false coordinates for the origin, and limits which would best suit the particular area. Consequently, various projections and ellipsoids have been employed. Nomenclature, sizes, predominant directions, and outlines of the grids vary considerably. This is demonstrated in Appendix D, which illustrates the layout of the nonstandard grids. This displays what is currently specified for new products and maintenance.

4-1.1.2 The nomenclature for the nonstandard grids includes the terms grid, zone, and belt to characterize the systems.

4-1.1.2.1 A grid covers a relatively small area. Its limits consist of combinations of meridians, parallels, loxodomes (rhumb lines), or grid lines. The origin of each grid is arbitrary. It is generally located approximately in the center of the grid and may bear no relation to the origins of other grids or to those of adjacent grids.

4-1.1.2.2 A zone usually is wide in longitude and comparatively narrow in latitude. Its limits, which are regular or in a few cases but irregular in most, consist of parallels and meridians. Each zone has its own origin which, with some few exceptions, falls within the limits of the zone. There is no relation between the origins of the zones, although, in a regional geographic area, those of adjacent zones may be on a common meridian or parallel.

4-1.1.2.3 A belt originally referred to a grid that was extensive in latitude, but narrow in longitude.

4-1.1.3 Each grid, zone, and belt has a name. Where groups of adjacent grids or zones cover a regional geographic area, the some name may be used for each; distinction is preserved by adding either a cardinal point or a number and a letter to the name.

4-1.1.4 The unit of measure is either meters or yards.

4-1.1.5 Normally, a British grid or zone is divided into 500,000-unit squares with each square identified by a letter of the alphabet. In a square composed of twenty-five 500,000- unit squares the letters are arranged alphabetically (the letter I is omitted) in a left to right - top to bottom fashion. Each 500,000-unit is similarly divided into twenty-five 100,000-unit squared, each of which is Identified by a letter following the some plan as for the 500,000-unit squares. The Normal Lettering Plan is illustrated in figure 11. This basic lettering plan is repeated for India Zone IIIA where it exceeds 2,500,000 yards in easting.

4-1.1.6 Among the British grids, deviations from the normal lettering system exist for the Irish Transverse Mercator Grid.

4-1.1.7 No letters are used for the Ceylon Belt, New Zealand Map Grid, Nord Algerie Grid, Nord Maroc Grid, Nord Tunisie Grid, Sud Algerie Grid, Sud Maroc Grid, and Sud Tunisie Grid.

4-1.1.8 The secondary grids are constantly changing. Specifications for those grids currently in this category are given in table 6.

4-1.1.9 The Gauss-Kruger (GK) projection and grids are the basis for the UTM grid system. Within the scope of this manual, there are three GK systems that may be encountered even though the Defense Mapping Agency uses none of them. The Russian GK grid is discussed in Department of the Army Field Manual No. 34-85, Conversion of Warsaw pact Grids to UTM Grids. General specifications are as follows:

Projection: Transverse Mercator in zones 6" wide.

```Ellipsoid:  Krassovskiy (a = 6,378,245 meters, 1/f = 298.3) (U.S.S.R., China to 1981).

Geodetic Reference System of China 1980 (a = 6,378,140 meters,
1/f = 298.257) (China from 1981).

Bessel (Germany).
```

Longitude of Origin: Same as the UTM.

Latitude of Origin: Same as the UTM.

Unit: Meter.

False Easting: 500,000 meter at the CM of each zone. However, the zone number is prefixed to the false easting In most cases, i.e. the false easting for the GK zone 7 is 7,500,000 meters.

False Northing: Same as the UTM.

Scale Factor on Central Meridian: Unity (1).

Grid Zone Designations: The zones are numbered eastward from 1 to 60 starting at the Greenwich meridian rather than the 180' meridian. In other words, the UTM and GK zones differ by 30. Row letters are not used with the GK systems Limits of System: The limits north and south are not rigidly defined as with the UTM. However, the limits can be assumed to be similar to the UTM.

Overlap: Same as the UTM.,

4-1.1.10 The specifications for the nonstandard grids, including the various lettering systems, are shown later in this chapter.

4-1.2 Nonstandard Grids on Maps and Charts.

4-1.2.1 Maps at scales of 1:100,000 and larger are gridded at 1,000-unit intervals. Those at scales 1:250,000 and 1:500,000 are gridded at 10,000-unit intervals. Maps at scales 1:1,000,000 and smaller than 1:500,000 are gridded at 100,000-unit intervals intersected by ticks at 10,000-unit intervals.

4-1.2.2 Each grid line, except on maps at 1:1,000,000 scale, is labeled with its value in the margin and on the line itself. Maps at 1:1,000,000 scale are not labeled on the face of the map. In the margins, the grid values for each line are shown in two sizes of type. The larger digits - the principal digits - are the only digits to be used in determining a grid reference. On the face of the map, the grid lines are labeled with principal digits only. These grid-labeling practices are similar to those of the UTM and UPS grids.

4-1.2.2.1 The number of principal digits labeling the grid lines is dependent upon the particular grid and the interval of the grid lines.

4-1.2.2.2 With grids whose 100,000-unit squares ore identified by letters or numbers, the 10,000-unit or 100,000-unit interval grid lines are labeled with one principal digit only. This represents the 10,000 digit of the grid value. On maps in the same area whose grid lines appear at 1,000-unit intervals, the lines are labeled with two principal digits. These represent the 10,000 and 1,000 digits of the grid value.

4-1.2.2.3 Except the Ceylon Belt, the lines of grids whose 100,000-unit squares are not identified are labeled with two principal digits when the interval is 10,000 and with three principal digits when the interval is 1,000 units. At the 10,000-unit or 100,000- unit interval, the numbers represent the 100,000, 10,000, and 1,000 digits of the grid value.

4-1.2.2.4 With the Ceylon Belt, two principal digits are used, regardless of the interval of the grid lines. On maps gridded at 10,000- or 100,000-yard intervals, the numbers represent the 100,000 and 10,000 digits of the grid value. On maps gridded at 1,000- yard intervals, the numbers represent the 10,000 and 1,000 digits of the grid value.

4-1.2.3 The 100,000- and 500,000-unit square identifications are shown in several ways, depending upon the scale of the map.

4-1.2.3.1 On maps at British origin which are gridded at 10,000-unit intervals, a miniature representation of the 100,000-unit grid lines is printed in the index to adjoining sheets. Within each square is added the 100,000-unit square identification. If the 500,000-unit squares are identified, the identification is added in smaller type just before each 100,000- unit square identification such as sC. Similar identifications appear on the face of the map. These will be found either in the center or at the corners of each 100,000-unit square. Variations in these practices will often be encountered.

4-1.2.3.2 This same, plan is followed on maps of British origin which are gridded at 1,000-unit intervals, although in many cases it will be found that the identifications are omitted from the face of the map.

4-1.2.3.3 On U.S. maps containing nonstandard grids, a miniature representation of the sheet with 100,000-unit grid lines appears in the grid reference box which is part of the marginal data of the sheet. The appropriate 500,000- and 100,000-unit square identifications appear in each square of the miniature. These are written together, with the 500,000-unit square,identification appearing in smaller type, such as sC. Examples are illustrated in figure 27. Similar identifications appear on the face of maps gridded at 10,000-unit intervals.

4-1.3 Referencing

Two basic methods for giving grid references are used on maps with nonstandard grid reference systems. These are modified in some instances. The first method, referred to as the normal British grid reference system, is used with grids whose 100,000- unit squares are identified by letters. The second method, referred to as the abnormal grid reference system, is used with grids whose 100,000-unit squares are not identified.

4-1.4 The Normal British Grid Reference System.

4-1.4.1 The instructions contained in this section apply only to those grids which adhere to the normal lettering plan.

4-1.4.2 The normal method for giving a reference based on a British grid is similar to that used for the U,S. Military Grid Reference System. See Figures 10 and 11. A reference consists of a group of letters and numbers which indicate (1) the 500,000-unit square identification, (2) the 100,000-unit square identification, and (3) the grid coordinates - the numerical portion of the reference - expressed to a prescribed refinement. It is desirable to leave a space between letters and numbers.

Examples:
NT 65 (Locating a point within a 10,000-unit square)
NT 6354 (Locating a point within a 1,000-unit square)
NT 632543 (Locating a point within a 100-unit square)

4-1.4.3 The use of the letters of the 500,000- and 100,000-unit square identifications depends on the size of the area of operations. The above examples of reporting are desirable when reporting between 500,000-unit squares so that ambiguity in letter identifications may be avoided. However, when all reporting is within a 500,000-unit square, the 500,000-unit square identification letter may be dropped, and the 100,000-unit square identification is retained to avoid ambiguity in numerical coordinates. When the area of operations is completely localized within a 100,000-unit square, both the 500,000- and 100,000-unit square identifications may be dropped.

4-1.5 Exceptions to the Normal British Grid Reference System.

4-1.5.1 The letter I is used as the 500,000-meter square letter with the Irish Transverse Mercator.

4-1.5.2 No 500,000- and 100,000-meter square letters are used with the New Zealand Map Grid. To avoid ambiguity, references are prefixed with the sheet number. A space separates the sheet number from the numerical reference.

Examples:
Z15 894623 (Locating a point within a 1,000-meter square at 1:50,000 scale)
Sht 5 989362 (Locating a point within a 10,000-meter square at 1:250,000 scale)

4-1.6 The Abnormal Grid Reference System.

4-1.6.1 The abnormal grid reference system is used when 100,000-unit squares are not identified, as with the Madagascar grid and the Lambert Grids of northwestern Africa. The reference usually is expressed in terms of grid coordinates only and is determined in the same manner as that used with the normal British grid reference system. The number of digits in the reference depends upon the grid interval and the grid itself.

4-1.6.2 Except for the Ceylon Belt, an abnormal reference taken from a map gridded at 100,000-meter intervals consists of four digits; at 10,000 meters, six digits; and for 1,000-meter intervals, eight digits.

Examples:
8645 (Locating a point within a 10,000-meter square)
863454 (Locating a point within a 1,000-meter square)
86324543 (Locating a point within a 100-meter square)

4-1.6.3 References based on the Ceylon Belt use four digits on maps gridded at 100,000- yard intervals and six digits for all other grid intervals.

```Examples:

Reference from map gridded at 100,000-yard intervals.
3524 (Locating a point within a 10,000-yard square)

Reference from map gridded at 10,000-yard intervals.
347241 (Locating a point within a 1,000-yard square)

Reference from map gridded at 1,000-yard intervals.
472413 (Locating C, point within a 100-yard square)
```

4-1.6.3.1 The Ceylon Belt grid reference system has a distinct disadvantage. Ambiguity between references is possible when six-digit reporting covers an area exceeding 100,000- yards square.

4-1.6.3.2 No official method is provided for preserving a distinction between the references. In practice, various devices have been used, such as prefixing the reference with the scale, name, or number of the map from which the reference was taken.

4-1.6.3.3 On maps prepared by the United States, the grid reference box will contain instructions for preserving distinctions. Normally, this will require prefixing the numerical reference with the sheet number of the map from which the reference was taken.

4-1.7 Unique Reporting.

Nonstandard reference systems, unlike the U.S. Military Grid Reference System, make no provisions for worldwide reporting. It may be necessary to identify the general areas in terms of geographic coordinates before giving the grid references for the separate general areas.

### 4-2 DIAGRAMS OF NONSTANDARD GRIDS.

The following pages show the diagrams and specifications of nonstandard grids used as the primary or secondary grid on maps produced by DMA:

Page 4-8 British National Grid

Page 4-10 Ceylon Belt

page 4-11 India Zone I

Page 4-12 India Zone IIA

Page 4-13 India Zone IIB

Page 4-14 India Zone IIIA

Page 4-15 India Zone IIIB

Page 4-16 India Zone IVA

Page 4-17 India Zone IVB

Page 4-18 Irish Transverse Mercator Grid

Page 4-19 Madagascar Grid

Page 4-21 New Zealand Map Grid (NZMG)

Page 4-22 Nord Algerie Grid

Page 4-23 Nord Maroc Grid

Page 4-24 Nord Tunisie Grid

Page 4-25 Sud Algerie Grid

Page 4-26 Sud Maroc Grid

Page 4-27 Sud Tunisie Grid

Page 4-28 West Malaysian RSO Grid

## CHAPTER 5 GEOGRAPHIC COORDINATE REFERENCES

### 5-1 USE.

The use of geographic coordinates as a system of reference is accepted worldwide. It is based on the expression of position by latitude (parallels) and longitude (meridians) in terms of arc (degrees, minutes, and seconds) referred to the Equator (north and south) and a prime meridian (east and west).

### 5-2 THE GEOGRAPHIC REFERENCE.

The degree of accuracy of a geographic reference is influenced by the map scale and accuracy requirements for plotting and scaling purposes.

```Examples of references are:

40°N 132°E (in degrees of latitude and longitude)
40°21'N 132°14' (To minutes of latitude and longitude)
40°21'12"N 132°14'18"E (To seconds of latitude and longitude)
40°21'12.4"N 132°14'17.7"E (To tenths of seconds of latitude and longitude)
40°21'12.45"N 132°14'17.73"E (To hundredths of seconds of latitude and longitude)
```

### 5-3 GEOGRAPHIC COORDINATES ON MAPS AND CHARTS.

5-3.1 U.S. military maps and charts include a graticule (parallels and meridians) for plotting and scaling geographic coordinates. Graticule values are shown in the map margin.

5-3.2 On most maps and charts at the scale of 1:1,000,000, the parallels and meridians are shown by intersections or full lines at one-degree intervals. The intersections or lines are labeled in degree values.

5-3.3 On maps and charts at the scale of 1:500,000, parallels and meridians are shown by full lines at 30-minute intervals. The full degree lines are labeled in degree values; the intermediate lines are labeled in minutes only.

5-3.4 On maps and charts at scales of 1:250,000 and larger the graticule may be indicated in the map interior by lines or ticks at prescribed intervals. The following indicates these intervals:

Scale Tick Interval Labeling at Corners1 Labeling of ticks
1:250,000 15 minutes Degrees-minutes 15 minutes
1:100,000 10 minutes Degrees-minutes 10 minutes
1:50,000 1 minute Degrees-minutes-seconds 5 minutes
1:250000 1 minute Degrees-minutes-seconds 5 minutes
1:12,500 1 minute Degrees-minutes-seconds 1 minute

1 When departing from standard sheet lines to avoid unnecessary sheets or because of datum changes, corners are labeled to 1 second for 1:250,000 and 1:100,000 scale and to 0.1 second for 1:50,000 to 1:12,500 scale.

5-3.5 On Joint Operations Graphics (JOG), between O° and 76°, meridians are shown by full lines at 15-minute intervals with 1-minute ticks. Between 76° and 84° North and between 76° and 80° South, meridians are shown by full lines at 30 minute intervals with 1-minute ticks.

### 5-4 THE WORLD GEOGRAPHIC REFERENCE SYSTEM

5-4.1 The World Geographic Reference System (GEOREF) is a system used for position reporting. It is not a military grid, and therefore does not replace existing military grids. It is an area-designation method used for interservice and interallied position reporting for air defense and strategic air operations. Positions are expressed in a form suitable for reporting and plotting on any map or chart graduated in latitude and longitude regardless of map projection.

5-4.2 The system divides the surface of the earth into quadrangles, the sides of which are specific arc lengths of longitude and latitude; each quadrangle is identified by a simple systematic letter code giving positive identification with no risk of ambiguity.

5-4.2.1 There are 24 longitudinal zones each of 15 degrees width extending eastward from the 180° meridian around the globe through 360 degrees of longitude. These zones are lettered from A to Z inclusive (omitting I and O). There are 12 bands of latitude each of 15 degrees height, extending northward from the South Pole. These bands are lettered from A to M inclusive (omitting I) northward from the South Pole. This code divides the earth's surface into 288 15 degree quadrangles, each of which is identified by two letters. The first letter is that of the longitude zone and the second letter that of the latitude band. Thus the major part of the United Kingdom is in the 15 degree quadrangle MK. See figure 12.

5-4.2.2 Each 15 degree quadrangle is sub-divided into 15 one degree zones of longitude, eastward from the western meridian of the quadrangle, these one degree units being lettered from A to Q inclusive (omitting I and O). Each 15 degree quadrangle is also subdivided into 15 one degree bands of latitude northward from the southern parallel of the quadrangle, these bands being lettered from A to Q inclusive (omitting I and O). A one degree quadrangle anywhere on the earth's surface may now be identified by four letters. Salisbury therefore is in the one degree quadrangle MKPG. See figure 12.

5-4.2.3 Each one degree quadrangle is divided into 60 minutes of longitude, numbered eastward from its western meridian, and 60 minutes of latitude, numbered northward from its southern parallel. This direction of numbering is used wherever the one degree quadrangle is located,i.e., it does not vary even though the location may be west of the prime meridian or south of the equator. A unique reference defining the position of a point to an accuracy of one minute in latitude and longitude (i.e., 2 kms or less) can now be given by quoting four letters and four numerals. The four letters identify the one degree quadrangle. The first two numerals are the number of minutes of longitude by which the point lies eastward of the western meridian of the one degree quadrangle, and the last two numerals are the number of minutes of latitude by which the point lies northward of the southern parallel of the one degree quadrangle. if the number of minutes is less than 10 minutes, the first numeral will be a zero and must be written, e.g., 04. The GEOREF of Salisbury Cathedral is MK PG 12 04. See figure 12.

5-4.2.4 Each of the one degree quadrangles may be further divided into decimal parts (1/10 th and 1/100 th) eastward and northward. Thus, four letters and six numerals will define a location to 0.1-minute; four letters and eight numerals will define a location to 0.01-minute.

## CHAPTER 6 PORTRAYAL OF GRIDS ON MAPS AT 1:100,000 SCALE AND LARGER

### 6-1 GENERAL.

6-1.1 Requirements for grid data and grid formats on maps prepared for the DoD at 1:100,000 scale and larger are essentially the same for Universal Transverse Mercator grids, Universal Polar Stereographic grids and nonstandard grids.

6-1.2 The grid data for DoD maps usually include the major grid, a declination diagram, a grid reference box, and notes identifying the grid.

6-1.3 The adjacent grid is provided as an overlapping grid when a map lies within approximately 40 kilometers of a grid junction line or a datum junction boundary. A separate declination diagram and notes identifying the overlapping grid appear in the margin for grid junctions, and may or may not appear for datum junctions, depending on grid alignments.

6-1.4 A map may show a secondary grid which occurs in the area. The secondary grid is identified by margin notes.

6-1.5 Normally, no single map of a foreign area in this scale category ever shows more than three grids. When a sheet covers an area which includes more than three grids (either major, overlapping, or secondary), those omitted are the ones which are considered of least military importance. Major grids are never omitted. When choice lies between two overlapping grids, the one retained usually is the one which occurs most frequently on the sheets in the general, area. Domestic maps may show up to five grids.

6-1.6 Specific dimensions, size and style of type, and placement of margin data relating to grids and grid formats at 1:100,000 scale and larger are contained in DMA product specifications.

### 6-3 MULTIPLE MAJOR GRIDS.

6-3.1 In certain instances a sheet contains more than one major grid.

6-3.1.1 With the UTM and UPS grids this may occur:

6-3.1.1.1 Where original sheet lines are retained as established by a mapping agency of a foreign country.

6-3.1.1.2 Where a sheet is shifted from the normal position to avoid making additional sheets.

6-3.1.2 With nonstandard grids, this condition occurs more frequently since, in addition to the above cases, grid junctions are sometimes loxodromes or are grid lines.

6-3.2 Grid, datum, ellipsoid, and zone junctions are indicated by accentuated lines, printed in black (blue for 1:100,000 scale). Labels identifying the junction appear parallel to and on each side of the junction line. The label may be shown more than once to facilitate identification. Each label is printed in the color designated for the particular grid system. When a grid, datum, ellipsoid, or zone junction line is coincident with a neatline, both the junction line and the identifying labels are omitted. If the junction line falls within 2.5 mm (0.10 inch) of the neatline, the junction line is not shown; it is considered as being coincident with the neatline.

6-3.2.1 For nonstandard grids, the label is modeled after the following:

```        WEST MALAYSIAN RSO GRID
SUD MAROC GRID
NORD TUNISIE GRID
MADAGASCAR GRID
```

6-3.2.2 The label for a UTM grid junction, or a UPS grid junction, includes the identification of the Grid Zone Designation and is written in MGRS terms as:

```        UTM GRID ZONE DESIGNATION: 47T
UPS GRID ZONE DESIGNATION: B
```

6-3.3 Each grid is shown by full lines Within its own area only, being represented at 1,000-unit intervals with every 10,000-unit line accentuated in weight.

6-3.3.1 On maps bearing two major grids, the extension of either grid into the area of the other (overlapping grid) is shown by outside ticks emanating from the neatline correctly aligned with its respective major grid. The even 10,000-unit ticks are accentuated in weight.

6-3.3.2 On maps bearing three major grids, a similar practice is followed, except that outside ticks are used to indicate the extension of the grid which occupies the major part of the sheet, and inside ticks are used to indicate the extensions of the others.

6-3.4 Grid values appear on all four sides of the sheet labeling each grid line and those grid ticks whose values are multiples of 5,000. Full values appear at each corner, labeling the first grid line in each direction from the corner.

6-3.4.1 For the UTM and UPS grids, the values for the different grids appear in black and blue. Block is reserved for the grid which covers the greater portion of the sheet. If the grid junction divides the sheet equally, black is used for the grid which occurs most frequently on the sheets in the general area. On maps at 1:100,000 scale, blue is used for the dominant grid and red-brown for the other grid.

6-3.4.2 For nonstandard grids, the values appear in the colors designated for the grid system. Where the designated colors are the same, one or more substitutions are made to emphasize distinction, with the order of preference as follows: black, blue, red-brown (or blue, red-brown, black at 1:100,000 scale).

6-3.4.3 Black is used for the UTM or UPS grids when either appears in combination with nonstandard grids. In such cases, if the conventional color for a nonstandard grid is black, a substitution is made for the nonstandard grid with blue, or red-brown being used. On maps at 1:100,000 scale, the order of colors is blue, red-brown, black.

6-3.5 Grid values, expressed in principal digits only, appear on the face of the map labeling each grid line. Refer to figures 15, 16, and 18 for sample treatments of the grid ladder numbers when a sheet contains more than one major grid.

6-3.6 Notes identifying each grid appear in the lower margin of the sheet. The notes are modeled after the following:

```       ELLIPSOID......................................WORLD GEODETIC SYSTEM
GRID.........................................1,000 METER UTM ZONE 47
(BLACK NUMBERED LINES AND TICKS)
1,000 METER UTM ZONE 48
(BLUE NUMBERED LINES AND TICKS)
```

6-3.7 When the ellipsoid is not the same for each of the grids shown on the map, the ellipsoids are included with the grid notes. The notes are patterned after the following:

```       GRID................1,000 METER UTM ZONE 31, INTERNATIONAL ELLIPSOID
(BLACK NUMBERED LINES AND TICKS)
1,000 METER UTM ZONE 32, CLARKE 1880 ELLIPSOID
(BLUE NUMBERED LINES AND TICKS)
```

6-3.8 Figures 15 and 16 illustrate the treatments described for sheets containing more than one major grid.

### 6-4 OVERLAPPING GRIDS.

6-4.1 An overlapping is generally required within approximately 40 kilometers of a grid, zone, or ellipsoid junction. The overlapping grid may be omitted if there are no land bodies within the 40 kilometer overlap area. See table 8.

6-4.2 The overlapping grid is shown by ticks printed in black (blue for 1:100,000 scale) emanating from the neatline correctly aligned with its respective grid and spaced at 1,000- unit intervals. The even 10,000-unit ticks are accentuated in weight. The direction of the ticks from the neatline (i.e., inside or outside) is dependent on the other grids shown on the map.

6-4.2.1 If the sheet contains one major grid, outside ticks are used.

6-4.2.2 If the sheet contains two major grids, inside ticks are used.

6-4.2.3 If a sheet contains two overlapping grids in conjunction with a single major grid, outside ticks are used for the overlapping grid which occurs most frequently on the sheets in the general area. Inside ticks are used for the other.

6-4.3 Values, similar in composition to those labeling the major grid lines, appear on all four sides of the sheet. The first grid tick in each direction from the southwest corner of the sheet whose values are multiples of 5,000 are labeled.

6-4.4 The color of the overlapping grid values is governed by the grid system. Where the prescribed color for two overlapping grids is the same, the color of the grid which occurs more frequently on the sheets in the general area is retained, and a substitution of black, blue, or red-brown, in that order of preference, is made for the other. (The order of preference for 1:100,000 scale is blue, red-brown, or black.) A similar substitution is made when the color of and overlapping grid is the some as the major grid.

6-4.5 Notes identifying overlapping grids appear in the lower margin of each sheet.

6-4.6 When the ellipsoid is not the same for the overlapping grid and the major grid, the ellipsoids are included with the grid notes. The notes are patterned after the following:

```     GRIDS....................1,000 METER UTM ZONE 42, WORLD GEODETIC SYSTEM
ELLIPSOID (BLACK NUMBERED LINES)
1,000 METER UTM ZONE 41, INTERNATIONAL
ELLIPSOID (BLUE NUMBERED TICKS)
```

6-4.7 Figures 17 and 18 illustrate the treatments described for sheets containing major and overlapping grids.

### 6-5 SECONDARY GRIDS.

6-5.1 Secondary grids are temporary grids whose purpose is to provide a common grid to adjacent maps and on companion maps of different scales. Generally, after one printing of the secondary grid, it will be discontinued. Excepted are those instances where mapping arrangements with cooperating foreign agencies specify the showing of a secondary grid. No more than one secondary grid is shown.

6-5.2 When required, the secondary grid is shown by inside ticks, printed in black (blue for 1:100,000 scale), emanating from the neatline in their correct alignment and spaced at -1,000-unit intervals. The even 10,000-unit ticks are accentuated in weight.

6-5.3 Values, similar in composition to those labeling the major grid lines, appear on all four sides of the sheet. The first grid tick. In each direction from the southwest corner of the sheet is labeled with full values. Thereafter, only those grid ticks whose values are multiples of 5,000 are labeled. If the secondary grid has a prescribed color, the color is used for the numbers unless there is conflict with another grid shown on the map. In that event, substitutions are made in the established order of preference.

6-5.4 A grid note, identifying the secondary grid, appears in the margin of the sheet.

6-5.5 When a secondary grid differs uniformly from the major grid, a coordinate shift note may be used in lieu of showing the secondary grid. The note should be patterned after the following:

```COORDINATE CONVERSION WGS 84 TO ED
Grid Add 30m.E., Subtract 9m.N.
Geographic:  Add 1.1" Long., Subtract 0.1" Lat.
```

6-5.6 Figure 19 illustrates the treatment described for sheets containing major and secondary grids.

### 6-6 THE DECLINATION DIAGRAM (ONE GRID).

6-6.1 A declination diagram appears in the margin of each sheet. The diagram shows the relationship of magnetic north and true north to grid north at the center of the sheet. It also provides information regarding the use of this data. See figures 20 and 21.

6-6.2 The diagram contains three prongs which emanate from a central point. These represent grid north, magnetic north, and true north, and are appropriately labeled.

6-6.2.1 The grid north prong is an extension of an easting (vertical) grid line; the extension is a continuous line, which stops at the central point near the bottom work limits of the sheet. The prong is broken for the letters GN.

6-6.2.2 The magnetic north prong emanates from the central point to the approximate extent of the letters GN. It Is surmounted with a half-arrowhead; a left half-arrowhead is used when magnetic north lies to the west of grid north, while a right half-arrowhead is used when magnetic north lies to the east of grid north.

6-6.2.3 The true north prong, surmounted with a five-point star, is shorter in length than the other two prongs. When it occurs as the left or right prong of the diagram, it emanates from the central point. When true north occurs as the middle prong, its characteristic star appears at the approximate height of the magnetic north arrowhead; the prong is shown as an extension from the central point.

6-6.2.4 Angles between the prongs are approximately represented. The magnetic north and true north prongs are plotted within 30 minutes of their given angular position from grid north, except that the magnetic prong is never shown within three degrees of the grid north prong. In maintaining relative symmetry between prongs, the characteristic star of the true north prong must never touch another prong. When there is no declination between prongs, a single prong represents the coincidence, and distinguishing characteristics (star, full arrowhead, or letters GN) of each are shown on the composite prong.

6-6.3 The grid-magnetic angle (G-M Angle) is expressed by a note alongside a dashed arc connecting the grid north and magnetic north prongs. The value of this angle is derived from the latest isogonic data for a standard epoch; i.e., a year that is divisible by five, such as 1990, 1995, etc. The value of the grid-magnetic angle is given to the nearest one-half degree with mil equivalent to the nearest ten mils. See Appendix A for a table of mil equivalents. 6-6.3.1 The grid-magnetic note is modeled after the following:

```1990
G-M ANGLE
7 1/2° (130 MILS)
```

6-6.3.2 For sheets with 0° grid-magnetic angle the note is shown as follows:

```1990
G-M ANGLE
0 (0 MILS)
```

6-6.3.3 For land insets, grid-magnetic data are shown only when the angle is different from that for the map proper. A diagram is not shown. The grid-magnetic data are shown by a note modeled after the following:

```GRID TO MAGNETIC DECLINATION
FOR 1990 IS 1 1/2° (30 MILS)
WESTERLY OVER THE ENTIRE INSET
```

6-6.4 The grid convergence is the angle between grid north and true north. The value of the angle is expressed to the nearest full minute, with the mils equivalent to the nearest one-half mil.

6-6.4.1 In the diagram, the grid convergence is indicated by a note alongside a dashed arc which connects the grid north and true north prongs. The convergence angle is given for the center of the sheet and is modeled after the following:

```GRID CONVERGENCE
1° 19' (23 1/2 MILS)
FOR CENTER OF SHEET
```

6-6.4.2 In land insets, a diagram is not shown. The grid convergence is shown only when the angle is different from that on the map proper. The convergence angle is given for the center of the inset and is modeled after the following:

```GRID TO TRUE NORTH CONVERGENCE
FOR THE CENTER OF THE INSET IS
1° 54' (34 MILS) EASTERLY
```

6-6.5 Notes appear in conjunction with the diagram explaining the use of the G-M Angle.

6-6.5.1 When the magnetic north prong of the diagram is east of the grid north prong, the notes read as follows:

```TO CONVERT A
MAGNETIC AZIMUTH
TO A GRID AZIMUTH
ADD G-M ANGLE

TO CONVERT A
GRID AZIMUTH TO A
MAGNETIC AZIMUTH
SUBTRACT G-M ANGLE
```

6-6.5.2 When the magnetic north prong of the diagram is West of the grid north prong, the notes read as follows:

```TO CONVERT A
MAGNETIC AZIMUTH
TO A GRID AZIMUTH
SUBTRACT G-M ANGLE

TO CONVERT A
GRID AZIMUTH TO A
MAGNETIC AZIMUTH
ADD G-M ANGLE
```

6-6.5.3 When the magnetic north and grid north prongs are coincident, azimuth conversion notes are omitted.

6-6.5.4 Azimuth conversion notes are not shown for insets.

6-6.6 The diagram and related notes are printed in the some color as the grid values.

Point of Contact: Geospatial Science Division
phone (314) 263-4486, DSN 693-4486
gandg@nga.mil

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