Australian Map Gridding (AMG) System

Australian Map Gridding (AMG) System

The grid system is composed of vertical and horizontal lines (grid lines) equally spaced and superimposed over a map. The distance between these lines is set at 1000 metres or 1 km. These lines are named as Eastings and Northings.

Eastings: • The horizontal lines which divide the map from WEST to EAST

• Eastings are read from west to east (left to right) with the value increasing towards the east.

Northings: • The vertical lines which divide the map from SOUTH to NORTH

• Northings are read from south to north (bottom to top) with the value increasing towards the north.

Where the Eastings and Northings intersect, is known as a grid reference. Grid references are measured as 4, 6 or 8 figures.

Grid Reference Numbers

Grid reference numbers are marked around the border of a map and are read with the Easting first followed by the Northing (start at the left of the map and read across to the Easting and then up to the Northing).

The following example shows the easting and northing references around the border of the map. 70 is the very top of the map Northing (horizontal line) and 63 is the first Northing up from the bottom of the map. 43 is the first Easting (vertical line) in from the left and 56 is the first Easting in from the right.

70 43 44 45 46 47 48 49 50 51 52 53 54 55 56

69

68

67

(A) 4768

4 Digit Rapid Number Easting = 47 Northing = 68 Accurate to 1000M (1km)

66

65

64

63

(B) 485664

6 Digit Rapid Number Easting = 485 Northing = 664 Accurate to 100M

(C)

8 Digit Rapid Number Divide these squares by another 10 x 10 block Accurate to 10M

• Four figure reference: Measure across the map to find 47 (easting) and then up the map to find 68 (northing) to create the grid reference of (4768).

• Six figure reference: To measure this you need to divide the grid reference square into a 10 x 10 block of squares which creates 100 squares inside the intersecting grid square. A grid reference can then be more accurately measured with a six figure reference. In the example, point (B) is measured as Easting 485 and the Northing 664 to create a grid reference of 485664.

• Eight figure reference: For an eight figure reference you will now need to divide the six figure squares into another 10 x 10 block of squares creating 100 squares inside the six figure reference squares. This will further refine the grid reference for more accuracy and would read as 48526642.

Degree of Accuracy

Accuracy increases as the figure of grid reference increases. • Four figure reference is accurate to within 1000 metres

• Six figure reference is accurate to within 100 metres

• Eight figure reference is accurate to within 10 metres.