Page 32 - 6589

GLOSSARY

Cartography – the art and science of producing maps, charts and other

representations of spatial relationships.
Contour – a line drawn on a map joining all the points on the Earth that are
the same height above mean sea level.

Coordinates – angular or linear values that designate the position of a point
in a given datum or projection system.
Coordinates, geographic – a system of spherical coordinates commonly
known as latitude and longitude.
Coordinates, grid – a plane-rectangular coordinate system expressed as

eastings and northings.
Datum – a mathematical surface on which a mapping and coordinate system
is based.

Elevation – the height above mean sea level.
Geocentric Datum – a datum which has its origin at the Earth’s centre of
mass. The advantage of the geocentric datum is its direct compatibility with
satellite-based navigation systems.
Geographical coordinates – a position given in terms of latitude and

longitude.
Global Positioning System (GPS) – is a satellite based navigation system
developed by the United States Department of Defense and widely used for

civilian navigation and positioning.
GNSS – Global Navigation Satellite System
Graticule – a network of lines on a map or chart representing the parallels of
latitude and meridians of longitude of the Earth.
Grid – two sets of parallel lines intersecting at right angles to form squares.

Grid convergence – the angular difference between Grid North and True
North.
Grid coordinates – the equally spaced vertical and horizontal intersecting

lines superimposed over the face of a map. One set of grid lines runs north-south,
while the other runs west-east. The position of a point on the map is described as
its distance east from a north-south line and its distance north of an east-west line.
Grid/magnetic (G-M) angle – the difference between grid north and
magnetic north and is a positive value if magnetic north it is east of grid north and

a negative value if it is west of true north.
30