2. General
• 1. As part of National Map Policy (NMP 2005), two series of maps are being published by
Survey of India, which are meant to replace the existing Everest Series Maps. Maps being published
as part of NMP 2005 are:
• (a) Open Series Maps (OSM).
• (b) Defence Series Maps (DSM).
• 2. The Open Series Maps (OSM) are devoid of the military grid, VAs/VPs and height/contour
data (in restricted areas). These are meant for civil agencies and are available for purchase,
commercially. The Defence Series Maps (DSM) are meant for exclusive use by Defence and Para
Military Forces. These maps contain all topographic information, and are classified as
restricted and above.
• 3. The contents and accuracy of Everest Series Maps
(currently in use) and that of Defence Series Maps are the same.
The DSMs are currently being prepared by mathematical
transformation (determined empirically) from Everest Series
Maps.
• 4. However there are certain changes in DSMs with respect to
the Everest Series Maps. These are explained in the succeeding
paras.
• Major Changes
• 5. Layout. The layout of Everest Series and Defence Series
Maps are different. The layouts are shown at Sketch P & Q
respectively.
3. 6. Everest Series Map Numbering. The map sheet
numbering in Everest Series is from 1 to 106. There are
no numberings for areas in sea, i.e. areas devoid of
land mass. Also, the numbers do not follow any standard
pattern and so, it is cumbersome to use them on computer
applications. The Everest Series numbering for India is
explained below:-
4. (a) Value of each main number, from 1 to 106 (39 to 88 for
India) is assigned to a 40 x 40 tile. In Figure 1, refer tile number
55. This tile is of size 40 x 40 and is divided into 16 equal tiles of 10
x 10 and each tile is assigned an alphabet from ‘A’ to ‘P’. Each of
these 10 x 10 tiles form a 1:250K scale map (also refer Figure 2).
A E I M
B F J N
C G K O
D H L P
5. (b) Each of the 10 x 10 tile(refer Figure3)is further
divided into 16 equal tiles of15’ x15’ each, and are
numbered from 1 to 16 (refer Figure 3). Each of these
15’ x 15’ forms a 1:50K scale map. Every 1:250K map
therefore contains 16 x 1:50K maps.
1 5 9 13
2 6 10 14
3 7 11 15
4 8 12 16
6. (c) Each of the 15’ x 15’ tile (refer Figure 4) is again
further sub divided into 4 tiles of 7.5’ x 7.5’. These 7.5’ x 7.5’
tiles represent 1:25K scale maps (refer Figure 4). Therefore,
every 1:50K map can be divided into 4 x 1:25K maps.
NW NE
SW SE
7. 7. DSM Numbering. The DSMs on the other hand, follow
an international system of numbering, which can be extended to
any part the world. The DSM numberings are different from
Everest Series Maps. However, for ease of reference, all
DSMs are printed with equivalent Everest Series Map
number also. For map numbering in DSMs, the world has been
divided into tiles of 60 x 40 (refer Figure 5). Each tile is assigned a
numeral for every 60 of longitude and an alphabet for every 40 of
latitude. The numerals in longitudinal direction (west to east)
begin from 1 at 1800 west longitude and extend up to 60 at 1800
east longitude. In the latitudinal direction, every 40 of latitude is
assigned an alphabet starting from ‘A’ at the equator and
alphabets increment towards the poles. On both the hemispheres
(north & south of equator), the same pattern is followed.
8. This method of map numbering is much simpler and logical. Using this
method, the numbering system can be extended to any part of the
world; which has been an inherent drawback in Everest Series Maps.
9. The numbering system in DSMs for India and adjacent countries is
explained in succeeding paras, with respect to equivalent Everest Series
numbering.
8. (a) As explained in Para 7 above, each 60 x 40 tile is
assigned a numeral and an alphabet in the longitudinal and
latitudinal direction, respectively. For the purpose of
elaboration, tile F44, highlighted by the shaded box in Figure 5 is
being used in the succeeding paras to explain the numbering system.
9. (b) The tile of 60 x40 falling between longitude and latitude as shown in Figure 6
is assigned values F & 44, as per DSM numbering convention explained at Para 7
above. So this tile is assigned the main value F44. This 60 x 40 tile is divided into 24
equal tiles of 10 x 10 and each tile is assigned an alphabet, starting from ‘A’ to ‘X’ (refer
Figure7). Each of these 10 x 10 tiles form a 1:250K scale map.
A B C D E F
G H I J K L
M N O P Q R
S T U V W X
78 84
24
20
6
4
10. (c) Each of the10x10 tile shown at Figure 7 are further
divided into 16 equal tiles of 15’ x 15’ each, and are
numbered from 1 to 16 (refer Figure 8). Each of these form
a 1:50K scale map. Every 1:250K map therefore, contains
16x1:50Kmaps.
1 5 9 13
2 6 10 14
3 7 11 15
4 8 12 16
F44H13 (1:50K scale map)
Note. F44H13 in DSM is equivalent to
55 N/13 on Everest Series
11. (d) Each of the 15’ x 15’ tile is also further sub divided into 4 tiles of 7.5’ x 7.5’
(refer Figure 9). Each of these 7.5’ x 7.5’ tiles represent a 1:25K map. Therefore, every
1:50K map can be divided into 4 x 1:25K maps.
F44H13/ NE (1:25K scale map)
Note. F44H13/ NE in DSM is equivalent to 55
N/13/ NE on Everest Series
12. Symbology.
There are very few changes in symbology of DSMs with
respect to Everest Series Maps. Few new symbols have been
added and few have been modified. The modifications of the
symbols have been carried out to make them self
explanatory and more user friendly. Unlike the Everest Series,
most of the important symbols have been displayed on the left
margin of all DSM maps with description. All changes in
symbology are shown at Appx A.
13. Military Grid Reference System.
• A rectangular grid coordinate system is required,
as computation of bearing, grid coordinates (in
northing & easting) and length can be easily
determined and a unique, brief yet precise
reference can be
made. The DSM grid zones (refer Figure 11) are of
size 60 x 80and all zones are of same size, unlike
the Everest Series (India & Adjacent Countries
Grid System) shown at Figure 10.
15. Projection & Datum
The map projection and datum of DSMs and Everest
Series maps are different. The DSMs are based on a global
datum on which positioning systems like GPS are based. On
the other hand, the Everest Series Maps are based on a local
datum, only suitable for the India & adjacent countries.
Details of the projection & datum are given below:-
Map Series Primary
Projection
Secondary
Projection
(Military Grid)
Datum
Everest
Series Polyconic Lambert
Conformal
Conical (LCC)
Everest
Defence
Series
Lambert
Conformal
Conical (LCC)
Modified LCC WGS-84
17. GR Values
• The GR (grid reference) of a point in DSM
and its corresponding Everest Series Map will
be different. This is
because of the change of datum & projection
as mentioned in
Para 11 above. However, the geographical
location of all points
will remain the same.
18.
19. Grid Letterings.
(a) Everest Series Maps. Any 6 figure GR
derived from a map would repeat in the same
grid zone after every 100 km. To overcome this
problem, all 6 figure GRs are prefixed by
two letters (alphabets), which make them
unique in that grid zone. These letters are
printed in the body of maps in bold fonts. It is
also likely that GRs prefixed with grid letters may
repeat in different grid zones. Again, to
counter this, the GR values already prefixed by
grid letterings are again prefixed by the grid
zone name.An e.g. is shown in Figures 14 & 15.
20.
21. Defence Series Maps.
• The grid letterings (as explained in Para 14(a) for DSMs have
been designed in a very simple way, unlike the Everest
Series. The grid letters have been designed keeping in mind
Digital environment. Details are explained in succeeding
paras.
• (i) Each DSM grid zone (refer Figure 11) is overlaid with a
military grid of size 1000,000 m x 1000,000 m for preparing
the military grid. These overlays are further sub-divided to
squares of 100,000 m x 100,000 m each (refer Figure 16).
These squares are numbered serially from ‘A’ to ‘K’
in both northing & easting direction, excluding alphabet
‘I’.
23. (ii) Any DSM map sheet falling in any of
these100,000 m x 100,000 m sized squares
(refer Figure 13) will be assigned grid letters as
per its geographic location on the grid zone. A
portion of DSM map sheet No H44O9 (62C9) is
shown in the Figure 17. From the full values
of northing & easting, it can be ascertained
that this map falls in the grid square denoted by
values (refer Figures 17, 18 & 19).
24.
25.
26. (iii) The GR values of any point falling on this map sheet
(H44O9) therefore would be prefixed by DSM grid zone 6F & grid
letter FJ. An eg is given vide Figures 20 & 21.
27. GR Conversion.
• For the ease of GR (grid reference)conversion
between Everest & Defence Series Maps, a
software utility has been developed by ADG
Military Survey (GSGS). This utility is called
‘GeoCalc’, and can be installed on any computer
for converting GRs from Everest to Defence Series
and vice versa. This software is meant strictly for
tri-services and can be obtained from ADG
Military Survey (GSGS). Methodology of using
GeoCalc is described at Appx B.
28. • For any further clarification on any issue
related to technical aspects of DSMs, ADG
Military Survey (GSGS) be approached.
