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Picture graphs use symbols (pictures) to represent data. A scale explains what each symbol represents—for example, one apple picture = 2 real apples. Scales are necessary when data quantities are large, making one-symbol-per-item impractical.
You already know how to read and create picture graphs where each symbol stands for exactly one item — a 1-to-1 picture graph. That works great when the numbers are small. But what if a school survey asked 120 students about their favorite subject, and you had to draw 120 symbols? The graph would be enormous. Scaled picture graphs solve this by letting each symbol represent more than one item, so the graph stays a manageable size.
The scale is the rule that tells you how many real items each symbol counts for. The scale is always shown in a key (also called a legend) somewhere on the graph, usually written like: "Each 🍎 = 5 apples." Once you know the scale, you can read the graph by multiplying: if the "Apples" row has 6 symbols and each symbol = 5, then 6 × 5 = 30 apples total. If a row has 4 symbols, that row represents 4 × 5 = 20 items. Reading a scaled picture graph is really a multiplication problem in disguise.
Sometimes a row will have a partial symbol — like half a picture. If the scale is "each symbol = 4," then half a symbol means 2. Partial symbols are just a visual way of representing amounts that fall between multiples of the scale. When you see a half symbol, divide the scale value in half to find what it represents.
Choosing the right scale when you create a graph is a decision that requires judgment. If your largest value is 30 and you use a scale of 1, you draw 30 symbols — too many. If you use a scale of 10, you draw 3 symbols — clean and readable. A good scale divides evenly into most of the data values, so you avoid awkward fractions. Thinking about scale is your first taste of the kind of design decisions that make data displays clear and useful.