Pitney Bowes MapXtreme - Manual (Page 579)

Appendix H: Elements of a Coordinate System
Projection Datums
MapXtreme v7.1 586 Developer Guide
Coordinate System Origin
The origin is the point specified in longitude and latitude from which all coordinates are referenced. It
is chosen to optimize the accuracy of a particular coordinate system. As we move north from the
origin, Y increases. X increases as we move east. These coordinate values are generally called
northings and eastings.
For the Transverse Mercator projection the origin’s longitude defines the central meridian. In
constructing the Transverse Mercator projection a cylinder is positioned tangent to the earth. The
central meridian is the line of tangency. The scale of the projected map is true along the central
meridian.
In creating a Hotine Oblique Mercator projection it is necessary to specify a great circle that is not
the equator nor a meridian. MapInfo does this by specifying one point on the ellipsoid and an
azimuth from that point. That point is the origin of the coordinate system.
Number Units
6 Centimeters
31 Chains
3
Feet (also called International Feet) *
* One International Foot equals exactly 30.48 cm.
2 Inches
1 Kilometers
30 Links
7 Meters
0 Miles
5 Millimeters
9
Nautical Miles †
† One Nautical Mile equals exactly 1852 meters.
32 Rods
8
US Survey Feet (used for 1927 State Plane) ‡
‡ One US Survey Foot equals exactly 12/39.37 meters, or approximately 30.48006 cm.
4 Yards