GPS receivers display a waypoint -- a specific position on the earth -- by
interpreting signals from a constellation of 24 NAVSTAR (NAVigation Satellite Timing and Ranging)
satellites put up by the US Dept. of Defense.
The satellites circle the earth every 12 hours.
Waypoints (WPS) are based on the UTM (Universal Transverse Mercator) projection
of the world defined by the
U.S. National Imagery and Mapping Agency (NIMA).
For example,
where actress Eva Gabor is buried in Westwood Cemetary in Los Angeles: Longitude 34.05.880 N,
Lattitude -118.44.145 W is equivalent to this GPS coordinate:
“11S" is equivalent to a 100,000-meter square area between Longitudes -120 and -114 degrees West and
Lattitudes between xxx and xxx degrees North.
“11" specifies a horizontal East-West location
on this grid which horizontally divides the 360 degree circumference of our world into increments of 6 degree each for
60 Zone Numbers, beginning half way around the world from the “prime meridian" near the British Royal Naval Observatory near London suburb of Greenwich, England.
“S" specifies a North-South location among
grid increments equivalent to 8 degrees above and below the equator.
The 20 zone Designations go alphabetically from “C" at the South Pole (-80 degree lattitude),
through “N" at the equator (zero degree lattitude),
to “X" (+80 degree lattitude) at “True North".
“I" and “O" are excluded to avoid confusion.
“0123456" is the Easting value of 12.3456 meters.
Using the NAD 27 datum,
a central meridian at the middle of each zone is assigned an easting value of 500,000 meters.
Easting values to the west of this central meridian are less than 500,000 meters (yards);
to the east, more than 500,000 meters.
“3772456" is the sample Northing value of 3777.456 meters.
Positive northing values measure the distance Northward from the equator.
Negative northing values measure the distance Southward from the equator.
To avoid confusion, UTM maps do not display digits after the decimal point and highlight the last two significant digits.
An Easting of 3772.456 appears as 3772.
GPS (Global Positioning Systems)
Don Bartlett's Practical Guide to GPS-UTM
Waypoints from other famous spots:
Download programs to convert between LL and UTM
Search the GNIS database of all names USGS uses on maps
