1.47.4 axis

set axis <axis> [ ( visible | invisible ) ]
  [ ( top | bottom | left | right | front | back ) ]
  [ ( atzero | notatzero ) ]
  [ ( automirrored | mirrored | fullmirrored ) ]
  [ ( noarrow | arrow | reversearrow | twowayarrow ) ]
  [ linked [item <number>] <axis> [using <expression>] ]

The set axis command is used to add additional axes to plots and to configure their appearance. Where an axis is stated on its own, as in the example

set axis x2

additional horizontal or vertical axes are added with default settings. The converse statements

set noaxis x2
unset axis x2

are used, respectively, to remove axes from plots and to return them to their default configurations, which often has the same effect of removing them from the graph, unless they are configured otherwise in a configuration file.

The position of any axis can be explicitly set using syntax of the form:

set axis x top
set axis y right
set axis z back

Horizontal axes can be set to appear either at the top or bottom; vertical axes can be set to appear either at the left or right; and $z$-axes can be set to appear either at the front or back. By default, the x1-axis is placed along the bottom of graphs and the y1-axis is placed up the left-hand side of graphs. On three-dimensional plots, the z1-axis is placed at the front of the graph. The second set of axes are placed opposite to the first: the x2-, y2- and z2-axes are placed respectively along the top, right and back sides of graphs. Higher-numbered axes are placed alongside the x1-, y1- and z1-axes.

The following keywords may also be placed alongside the positional keywords listed above to specify how the axis should appear: