__SALIENT FEATURES OF POLYCONIC PROJECTION__

- All parallels are projected without distortion (Scale is exact along all parallels)
- Parallels are arcs of circles but they are not concentric
- It is neither conformal nor equal area
- Central meridian and equator are straight lines; All other meridians are complex curves
- There is NO DISTORTION ONLY AT CENTRAL MERIDIAN
- It is used in India for all topographical mapping on 1:25,000; 1:50,000 and 1:250,000 scales

The disadvantages of this projection are listed below:

- It can have a rolling fit only
- Meridians and parallels do not intersect at right angles
- Inability to show seamless data in a rectangular coordinate system

The polyconic projection is not being used for mapping anywhere in the world except India and a few adjacent countries.

__SALIENT FEATURES OF LAMBERT CONFORMAL CONIC PROJECTION__

- It is a conical projection
- It is conformal
- Parallels are unequally spaced arcs of concentric circles, more closely spaced near the center of the map
- Meridians are equally spaced radii of the same circles, thereby cutting parallels at right angles
- Scale is true just along two standard parallels or along just one
- Intersection of central parallel and central meridian is the origin of rectangular coordinate system
- Central meridian is Y-axis and a line perpendicular to it is X-axis
- A large value is given to the origin so that ALL coordinates for the projection are POSITIVE
- The origin assumes a value (0,0) is also known as
__'FALSE ORIGIN'__

__SALIENT FEATURES OF TRANSVERSE MERCATOR PROJECTION__

- It is a widely used conformal projection
- It is a cylindrical projection
- It is conformal
- The central meridian, each meridian 90 degrees from the central meridian and equator are straight lines
- Other meridians and parallels are complex curves
- Scale is true along central meridian or along two straight lines equidistant and parallel to central meridian
- Scale becomes infinite 90 degrees from central meridian
- It is used extensively for quadrangle maps at scales 1:24,000 to 1:250,000
- It was presented by lambert in1772
- It is not used in India but extensively used in USA
- The State Plane Coordinate System (SPCS) is based on the Transverse Mercator Projection in USA for states with North-South extent
- It is used for quadrangle maps in the USA
- It is used for army map service in the USA
- Ordnance Survey of Great Britain switched to transverse mercator from cassini
- It is used in Canada in three zones.

__SALIENT FEATURES OF UNIVERSAL__

__TRANSVERSE MERCATOR__

__PROJECTION__

- It is a particular case of transverse mercator projection
- Transverse mercator in this projection is 6 degrees wide
- Reference ellipsoid for North America was given by Clark in 1866
- Central meridian is the origin for the longitude
- Equator is the origin for the latitude
- Unit for distance is metre (m)
- False northing is 0m for northern hemisphere and 10,000,000m for southern hemisphere
- False easting is 500,000m
- Scale factor at central meridian is 0.9996
- Zone numbering begins at 1 for zone between 180 W and 174 W and increases to 60 for zone bounded by meridians 174 E and 180 E (Each zone 6 degrees wide)
- Latitude limits 80 N and 80 S
- Nearly 60 countries use this projection as the general use projection within the country
- It is NOT the universal projection for all countries.
- In India, it is used by NAVAL HYDROGRAPHIC SURVEYS for their maps and charts

**Conversion among coordinate systems are carried-out mathematically using map projection equations and their inverses.**