Fundamentals of Statistics contains material of various lectures and courses of H. Lohninger on statistics, data analysis and here for more.

Dot Plot

Dot plots are drawn by placing a symbol for each observation of a variable X at the corresponding position along a number line (Fig. A). However, this approach exhibits the drawback that equal observations are plotted on top of each other, thus creating a wrong impression of the distribution of the observations (especially when many observations are to be displayed).

For that reason this kind of plot is most often drawn as a stacked dot plot where equal observations are displayed as a stack (Fig. B).

If we replace the dot symbols by lines of a specific length we obtain line diagrams (Fig. C) which allow to draw more observations than stacked dot plots. However, line diagram must not be mixed up with histograms.