Step line charts are single-series charts with a line passing through and connecting individual scatter points at (x, y) cartesian coordinates. There is no diagonal line: all continuous segments joining these points are broken into a vertical and a horizontal portion, in a stairs effect. All segments have the same series color. The points are eventually highlighted - with markers - when the mouse moves over them.
Our US Sales demo charts show a step line joining the points at the intersection of each year value between 2000 and 2017 and the number of products sold in US in that year. There are one horizontal and one vertical segment between every two consecutive data points. The horizontal X baseline appears here as a category axis, with regular intervals for each year value. Line charts use also often a linear baseline, with X values distributed at random intervals.