Reversing legend order
To turn this option on or off, navigate to the Marks menu, and select the Reverse legend order option.
In the case of distinct dimension mapping, the default legend appears in ascending alphabetical order; reversing it renders the legend in descending alphabetical order. Note that the dimension-color mapping remains the same.
For graphs that map a continuum of values, such as choropleth maps, the legend shows a sliding scale of color and values at the minimum, median, and maximum. The reverse legend option simply changes the orientation of the legend from maximum value on top, to minimum value on top.