Spatial Referencing Systems
Maps locate and reference information first on a local basis - within the map frame, and on a global
basis - on the Earth, using a geographic referencing system which has the following qualities :
applicable to any point on the earth, therefore universal.
applies to all scales of maps, thus flexible.
easy to understand and follow.
does not require any previous knowledge of the area.
will reference a point to any degree of accuracy which is scale related.
Coordinates:
The distances of a surveyed point, north/south and east/west from the origin of survey. Although the
word coordinate is usually taken to mean horizontal position (x and y coordinates), the position of a
point is not fully defined unless the elevation above the datum, or vertical coordinate (z coordinate), is
also provided.
Spherical Coordinate:
Latitude, Longitude are known as spherical or geographical coordinates. Excellent for a spherical shape
(the Earth), but difficulties arise when used on a flat surface.
Round earth to a flat surface.
Meridians converge at the poles
Parallels are complex curved lines.
Angular measurement - degrees, minutes and seconds.
Units of measurement - 360 degrees, 60 minutes, 60 seconds.
Plane Coordinates:
Plane co-ordinates simple solution of x,y co-ordinates. A rectangular grid consists of a series of straight
parallel lines, that are evenly spaced, intersecting at right angles, forming a series of same sized squares.
Good for determining absolute and relative positions.
Used in digitizing.
Hand plotting of map projections using a drafting table and T-square
Georeferenced to a common co-ordinate system.
Polar Coordinates:
A radius distance and angular measurement to a point referenced from a north/south line of reference.
Good for determining relative positions.
Used in map construction.
Hand plotting of map projections using a drafting table and T-square
Georeferenced to a common co-ordinate system.
Universal Transverse Mercator Grid:
A plane grid based on the U.T.M. projection, used to locate positions on a map.
based on Transverse Mercator Projection.
uses a plane grid, squares, superimposed on the irregular shaped graticule
from 800 South to 840 North, 1800 West to 1800 East.
sixty 60 zones.
each zone covers 1 million metres E/W and 20 million metres N/S.
Block Grids:
Most common grid type. Simple row and column format to locate information within a block.
fast and easy.
no fancy mathematics involved.
no restrictions to size, shape or scale.
not very accurate.
reduces search time but not projected reference system.
Nominal Identification:
Using proper names to locate an area. Most common method for identifying areas. Not a reference
system but works most times.
knowledge of area mandatory.
not specific.
Mapping Home
GIS Home