A dumbbell chart: its rows, and what its two ends are called.
An object rather than a bare array -- as HeatmapData and
GaugePoint already are -- because the names of the two ends belong
to the chart and not to any one row. Repeating them on every point would
let a producer emit rows that disagree about what the chart is comparing.
Those names are the content of the comparison. Announced as "start" and
"end", a chart of life expectancy in 1990 against 2020 tells the reader
which dot they are on and not which year it is, which is the one thing the
legend gives a sighted reader for free.
A dumbbell chart: its rows, and what its two ends are called.
An object rather than a bare array -- as HeatmapData and GaugePoint already are -- because the names of the two ends belong to the chart and not to any one row. Repeating them on every point would let a producer emit rows that disagree about what the chart is comparing.
Those names are the content of the comparison. Announced as "start" and "end", a chart of life expectancy in 1990 against 2020 tells the reader which dot they are on and not which year it is, which is the one thing the legend gives a sighted reader for free.