Coordinate systems enable geographic datasets to use common locations for integration. The most commonly used coordinate system today is the latitude, longitude, and height system. The Equator and the Prime Meridian are the reference lines used to measure latitude and longitude. The equator which lies halfway between the poles is a natural reference for latitude. A line through Greenwich, England, just outside London, is the Prime Meridian.
Projected coordinate systems and geodetic data are used in geodesy, navigation, surveying by cartographers and satellite navigation systems to translate positions indicated on the products to their real position on earth. The systems are needed because the earth is an imperfect ellipsoid. Localised datums can give a more accurate representation of the area of coverage than the global WGS 84 datum. SVY21, for example, is a better approximation to the Geoid covering Singapore than the global WGS 84 ellipsoid. The projected plane coordinate systems map the earth's spherical surface onto a twodimensional Cartesian coordinate plane. Thus, projected coordinate systems are referred to as map projections.
The plane coordinate system is based on the Transverse Mercator projection from geographical coordinates referenced to the WGS84 ellipsoid.
The origin of projection is an unmarked point having the following geographical coordinates referenced to the WGS84 ellipsoid.
Longitude 
103° 50' 00" 
Latitude 
1° 22' 00" 
False Origin ( Easting ) 
28001.642 m 
False Origin ( Northing ) 
38744.572 m 
Scale Factor at Central Meridian 
1.00000000 
The reference spheroid is the WGS84 ellipsoid with the following definition:
Semimajor axis 
6378137.0000 m 
Semiminor axis 
6356752.3142 m 
Flattening 
1/298.257223563 
Eccentricity 
0.081819191 
"SVY 21" is a geodetic coordinate datum based on the WGS84 ellipsoid and a reference point known as BASE7 (located at Pillar 7 Pierce Reservoir) with values fixed at:
Longitude 
103° 49' 31.975227" 
Latitude 
1° 22' 02.915414" 
Ellipsoidal height 
26.824 m 
Reduced level (PLD) 
17.113 m 
Geoidal Undulation 
9.711 m 
Projection 
Transverse Mercator 
Projection Origin (Unmarked point) 
Longtitude 
103° 50' 00" 
Latitude 
1° 22' 00" 

False Coordinates of Projection Origin 
Easting 
28001.642mE 
Northing 
38744.572mN 
