Representations are the interface between the data coming from the user and the rendered output.
Each type that implements
CategoricalRepresentation knows how to read in data
and convert that into a concrete element to be incorporated into a larger plot.
For example the
scatter::Scatter representation can be created from a list of coordinates.
to_svg() is called on it, it will create the SVG elements showing the points from within
the range that was requested by the caller.
These points may then be layered with other SVG elements from other representations into a
A representation of data that is categorical in the x-axis but continuous in the y-axis.
A representation of data that is continuous in two dimensions.