This attribute controls the appearance of an annotated
coordinate grid (drawn with the AST_GRID routine) by determining
the linear interval between the "major" axis values of a Plot, at
which (for example) major tick marks are drawn. It takes a separate
value for each physical axis of the Plot so that, for instance,
the setting "Gap(2)=3.0" specifies the difference between adjacent major
values along the second axis. The Gap attribute is only used when
the LogTicks attribute indicates that the spacing between major axis
values is to be linear. If major axis values are logarithmically spaced
then the gap is specified using attribute LogGap.
The Gap value supplied will usually be rounded to the nearest
"nice" value, suitable (e.g.) for generating axis labels, before
use. To avoid this "nicing" you should set an explicit format
for the axis using the Format(axis) or Digits/Digits(axis)
attribute. The default behaviour is for the Plot to generate its
own Gap value when required, based on the range of axis values
to be represented.