About Map Numbering
1:1 Million and 1:250 000 Scale Numbering
Standard topographic maps are numbered using a system developed for the International Map of the World. Map areas at 1:1 million scale are identified by a two letter combination which identifies the hemisphere and a four degree band of latitude and a two digit number which identifies a six degree band of longitude. This grid is shown on the small map of Australia in the 1:100 000 and 1:250 000 Scale Index Map 2008 [PDF 844KB]. For example, the 1:1 million scale map covering Sydney is numbered SI56.
Each 1:1 million scale map is divided into 16 rectangles, 1 degree of latitude by 1.5 degrees of longitude. These rectangles define the standard 1:250 000 map areas. These areas are numbered left to right and top to bottom. Combining the 1:1 million number and the number of the rectangle produces the 1:250 000 scale map number. For example, the map number for 1:250 000 scale Melbourne map is SJ5505.
In Australia, a number of 1:250 000 scale maps vary from strict adherence to this system to reduce the production of maps which only cover small areas of land. Maps which significantly vary from the system are identified as 'special' in the name, for example Fraser Island Special. The map number is the map number of the standard area contributing the greatest land mass to the special map. In the case of Tasmania a four sheet system replaces the standard grid and the sheets are identified, North-west, North-east, South-west and South-east.
1:100 000 Scale Numbering
Sheet numbers at 1:100 000 scale are four digit numbers. The first two digits define a longitude band 0.5 degree wide and the second two digits a latitude band 0.5 degree wide. Six 1:100 000 scale map areas nest into a standard 1:250 000 scale sheet areas. The following diagrams illustrate the numbering for 1:100 000 scale maps and 1:50 000 scale maps.
1:50 000 Scale Numbering
Sheet numbers at 1:50 000 scale are five digit numbers. Four 1:50 000 scale map areas nest into a standard 1:100 000 scale sheet areas. The first four digits are the 1:100 000 scale number, the final digit is numbered 1-4 clockwise from the top right hand quadrant.