A column of numbers is hard to feel; a picture is instant. Charts turn data into shapes so patterns leap off the page — which category is biggest, which is rare, how the whole splits up. The three you need to read and draw are bar charts, pictograms and pie charts.
Why this matters: charts are how the world actually shows you data — in the news, in adverts, on a phone's battery screen. Reading them correctly (and spotting a misleading one) is a life skill, and drawing them accurately is a staple of every exam paper.
Bar charts and pictograms
- Bar chart — the height of each bar shows the frequency, so taller means more. Bars sit apart with gaps and let you compare categories at a single glance.
- Pictogram — a picture symbol stands for a set number, and you count the symbols. It's like using coins: if one coin means 5p, three coins mean 15p. A half symbol means half that value.
Pictogram where an apple symbol = 4 apples: 3½ symbols means 3 × 4 + 2 = 14 apples (three full symbols give 12, and the half gives 2).
Pie charts
A pie chart shows each category as a slice of one full circle. The whole circle is 360° and stands for the whole data set, so each slice's angle is that category's share of the total:
Angle of a slice = (category ÷ total) × 360°
Out of 40 people, 10 chose pizza: angle = (10 ÷ 40) × 360 = 90° — a quarter of the circle, which makes sense because 10 is a quarter of 40.
It works in reverse too: given a slice's angle, you can find how many people it represents. A 72° slice is 72 ÷ 360 = ⅕ of the people; if the total is 30, that slice = 30 ÷ 5 = 6 people. Reverse rule: people = (angle ÷ 360) × total.
| Chart | Shows frequency by… | Best for… |
|---|---|---|
| Bar chart | height of the bar | comparing separate categories |
| Pictogram | number of symbols | friendly, quick displays |
| Pie chart | angle / size of the slice | showing shares of a whole |
Common mistake: on a pie chart, remember the angles must total 360°, not 100 — and on a pictogram, always check the key first. Miscounting a half-symbol, or forgetting one symbol equals several items, throws the whole reading out.
In a nutshell: bars use height, pictograms use symbols (one symbol = a set value, so mind the key), and pie-chart angles = (part ÷ total) × 360° — run it backwards to turn an angle into a count.