1. data measure: the graphical element that actually locates or plots the data is the data measures.
like, the bars of a bar plot; the dots of a scatterplot; the dots and the dashes of a dot-dash-plot and so on.
the ink of the data measure can itself carry data. Building data measures out of the data increases the quantitative detail and
dimensionality of a graphic. ( link to a third, fourth variable)