Map blocks and map units are based on a system originally devised by the British

Ordinance Survey. Each 1:1 million scale map sheet is subdivided into 3456

graticular map blocks, each measuring 5’ of latitude by 5’ of longitude. These map

blocks are further subdivided into 25 1’ by 1’ map units. A map unit is approximately

3 square kilometres in size.

Map blocks and map units are used in New South Wales to define certain types of

titles. Petroleum exploration titles (PELs) are applied for and granted as a series of

map blocks (Map sheet, block number), and mineral exploration titles, which tend to

be smaller in size, are defined as a list of map units.