Definition
Key of a data display
A key explains what the symbols, colours, marks, or intervals in a data display represent.
What it means
A key is the decoder for a graph or chart. Read it before you count or compare. In a pictogram, one picture may stand for several objects, so the key tells you the value of each picture.
Remember it
Read the key first: it tells you what the display’s marks mean.
Example
A book pictogram has the key “one book icon = 4 books.” A row with 3 book icons represents 3 × 4 = 12 books, not 3 books.
Watch for
A title says what the display is about; a key says what its symbols or colours represent.
Common mix-up
Do not assume one picture means one item. The key may give a different value.
Exact meaning
The key of a data display maps a visual feature—such as a symbol, colour, mark, or interval—to the category or quantity it represents. A key is needed whenever that meaning is not already clear from the display.