A sparkline is a small line chart with no axes, no labels and no grid, set at the size of a word and placed inside a table row or a sentence. Tufte introduced them in Beautiful Evidence (2006) as data-intense graphics placed in the flow of text. They add shape to a number that a table gives only as a level.
Why add a sparkline column to a table?
The case for a sparkline column is a ranking that changes with what you rank by. Turant's seven named cities, ranked by contribution margin per order in the latest quarter, run Mumbai ₹17.25, Ahmedabad ₹16.05, Bengaluru ₹15.55, Hyderabad ₹13.95, Pune ₹12.75, Delhi NCR ₹12.15, Chennai −₹9.75. That's the level ranking, and it's what a table's last column gives you. Rank the same seven by their gain over the last two quarters and the order changes: Ahmedabad ₹17.00, Delhi NCR ₹15.00, Hyderabad ₹14.20, Bengaluru ₹14.00, Mumbai ₹13.50, Pune ₹9.70, Chennai ₹7.50.
Two rows move a long way. Mumbai is first on level and fifth on slope, because its early lead is being competed away. Delhi NCR is sixth on level and second on slope. It started ₹20.07 below zero in Q3 and is closing faster than every named city except Ahmedabad. A level column shows neither. A sparkline column shows both, in the width of a word, and the reader doesn't have to do any arithmetic.
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How do you build a sparkline column, and when does it fail?
Four rules make a sparkline column work. First, one scale across the whole column, or the shapes aren't comparable. The same free-scaling arithmetic applies here: the flattest row, Chennai at a range of ₹14.92, would be exaggerated 3.13 times against the column's shared span of ₹46.72 if it got its own scale. Second, label one endpoint, usually the last value, so the reader can anchor the shape to a number. Third, add a reference band or line where a threshold matters. For this table that's zero, since crossing it is the event. Fourth, no axis furniture at all, because a sparkline that grows tick marks has become a small bad chart.
It's worth knowing where they fail. A sparkline can't show a precise value, so it never replaces the number. It goes beside it. It needs at least five or six points to have a shape, and with three it's a slope with delusions. And it won't survive a projector at the back of a room, which makes it a device for documents and screens read at desk distance. Keep it off presented slides.
What is in-line data in a sentence?
In-line data in a sentence is the same idea at a smaller scale. Say the network figure was ₹12.37, with the eight city figures spanning −₹9.75 to ₹17.25. That puts three numbers in a clause and saves you an exhibit. A sentence holds about three numbers before it stops being a sentence, and the fourth number is your signal to build the table.