This option is used to initialise the world coordinate mapping to a simple pixel-based system. This initialisation must be done before specifying a new world coordinate system.
In addition to the initialisation, this option also requests specification of the units of length related to the world coordinate system. These units are used for information purposes only: some DigImage features include the units of measure in some forms of output. These units may be changed without initialisation using [U Specify length units].