The chart displays a matrix. The marker represents the value at each intersection. 

At first glance this chart may appear very similar to the Tile chart and to some extent it is. But this chart uses a different approach to the construction of axis labels, markers and the conditional formula.

The chart is based on a XY-Scatter with series used to provide axis labelling and the  spots. The chart uses data from conditional formula in order to display a single spot in each position.

The workbook contains a step by step explanation on how to construct the chart.