By default, charts plot data accross the x-axis in an enumerated manner. The spacing is even between each point (row) returned in the DataLayer. This is "Standard" scaling. This works fine in many cases, especially when there are no missing data points. "Linear" scaling plots points according to an x-axis value. The x-axis spread evenly end-to-end, even though the data points are not. Linear spacing works with either numeric or date/time values.
Linear scaling is only appropriate for Line, Area, Spline and Polar charts.