"values on each axis) are drawn across the plotting area.
If the Grid value of a Plot is non-zero, then grid lines will be drawn. Otherwise, short tick marks on the axes are used to mark the major axis values. The default behaviour is to use tick marks if the entire plotting area is filled by valid physical coordinates, but to draw grid lines otherwise.
The spacing between major axis values, which determines the spacing of grid lines, may be set using the Gap(axis) attribute.