Not advisable to stick
to weak datum:
LT GEN SURINDAR
P MEHTA
Questions have been raised at various
quarters whether the Vision invoked
by the President can be fulfilled
by using 19th century Datum.
Before I comment on this, let us
review briefl y the broad classifi cation
of Mapping /Cartographic effort
required for various applications.
• Cartography for Global level
planning and execution. This calls
for most accurate techniques to
depict the shape and size of the
earth. Requires most accurate
absolute positioning of points on
globe to ascertain correct distance,
directions, areas, volumes, essential
for various global activities such as
Global Warfare, Continental Drift,
etc. Also involves very precise
measurements of International
boundaries. There is the requirement
of most precise control network
based on well defi ned Datum.
• Cartography for Macro level
planning and execution. Requires
depiction of all major topographical
details (both physical and manmade)
relatively correct to enable macro
level study and planning of land
related activities. Topographical
maps on scale 1:25000 to 1:250000
have been used. Relative accuracy is important and distance, area
and volume can be computed
within limited accuracy, generally
acceptable for macro level
planning. Any suitable cartographic
projection with any reasonable
datum can serve the purpose.
• Cartography for Micro level
planning and execution. This
requires all terrain data accurate
in size and shape in relative
correct position so as to get
true distance, area and volumes
for micro level planning and
execution of land related projects.
These are large scale maps of the
small area of interest. Some of
the Engineering projects ( such
as Irrigation) , require study on
map scale 1:5000 to 1:10000 and
further detailed planning, design
and execution on larger scale
(1:1000 or even larger). Relative
accuracy of positioning of details
is the prime requirement and
absolute positioning and well
defined datum is not mendatory.
Let us now examine major inputs
required for various requirements
projected by the President.
Providing Urban Amenities
in Rural Areas
Requires mapping on large scale
(1:10000 or larger 1: 2000) for
7000 PURAS (6 lakhs villages / 2
lakhs panchayats) in 2 years time.
Requires huge survey and mapping
effort. It is advisable to collect
terrain data based on the existing
control network , rather than waiting
for any new Datum defi nition