An Axis defines the numeric range covered by one axis of the plot, as well as that axis' appearance: line style, TickMarks, and label. Note that one Axis can have many sets of TickMarks, each with a different size, style, and label; this is how Graphite implements major and minor tickmarks and grid lines. Each Axis can specify a list of drawing locations. There are constants for putting axes along the graph frame. Datasets are mapped to a set of 3 axes through an axis mapping. The list of axes mappings are associated with Datasets with the same mechanism used in assigning PlotFormats to Datasets (round-robin).