What Are Charts?
A chart is a way of turning numbers into a picture so that a difference you would have to calculate becomes something you can see. This page explains what charts are, the handful of jobs they do, and gives you a four-question chooser that ends in a specific recommendation.
Which chart should I use?
Answer three questions and the chooser names a shape, says why, and shows a working example with real numbers.
What is the number doing?
How many categories or points?
How many series?
Use a bar chart
Because: A few categories on one shared scale: bar height maps straight to value, so the comparison needs no decoding.
Watch out for: When values cross zero, keep the zero baseline so negatives read as negative.
A working example
What a chart actually is
A chart maps numbers onto something visual: the length of a bar, the position of a point, the angle of a slice, the shade of a cell. Your eye then compares those visual properties far faster than it could compare the digits. That is the whole trick — and it is also where charts go wrong, because some visual properties are easier to compare accurately than others.
Length along a shared baseline is the most accurate, which is why bar charts are so hard to beat. Position on a common scale comes next, which is what makes line and scatter charts work. Angle and area are much weaker, which is why a pie chart with eight similar slices tells you almost nothing. Colour intensity is weaker still — fine for spotting a pattern in a heatmap, useless for reading a value.
The five jobs charts do
- Comparison: which category is bigger? Bar chart, horizontal bar chart.
- Trend: how has this moved over time? Line chart, area chart.
- Composition: what share does each part take of the whole? Pie, donut, stacked bar.
- Distribution: how are the values spread out? Histogram, box plot.
- A single headline number: no chart at all — a stat tile with the number and its change.
Chart vs. graph vs. plot
In ordinary use these are interchangeable. "Graph" tends to be used in school and in mathematics, "chart" in business, "plot" in science and statistics. Nobody will misunderstand you whichever you pick. The distinctions that actually matter are between chart types — bar versus line versus pie — not between the three words.
Four rules that fix most charts
- Start bar charts at zero. Length is the message, so a cut-off axis is a distorted message.
- Label the unit. "63,400" is not a number until the reader knows whether it is dollars, sessions or seconds.
- Sort on purpose. Alphabetical order is almost never the most useful order for a ranked comparison.
- One chart, one point. If a chart needs a paragraph to explain, it is probably two charts.
Frequently asked questions
What are charts used for?
To make a quantitative comparison visible at a glance: which is bigger, how it changed, what share each part takes, and how the values are spread.
What is the difference between a chart and a graph?
In everyday use, none. The meaningful difference is between chart types — bar, line, pie — not between the words.
Which chart type should I use?
Start from the question. Comparing categories means bars, movement over time means a line, share of a whole means a pie or a stacked bar, one headline figure means no chart at all. The chooser on this page asks four questions and names a type.
How many series is too many?
For lines, roughly four before the chart turns to spaghetti. For grouped bars, two — three at a push. Beyond that, split into small multiples.
See worked chart examples
Upload an Excel or CSV file and get charts with a checkable answer behind every number.