Temperature over a day. Stock price over a year. Your weight over a decade. When the x-axis is time, a line graph turns a column of numbers into a story with a plot.
A line graph plots data points and connects them with lines. It's built for showing how something changes over time (or another ordered variable).
Trends, forecasts, before/after comparisons, growth curves, monitoring dashboards — line graphs are the language of 'over time'.
Reading a line graph
- Upward slope = increasing; downward = decreasing.
- Steepness = rate of change — steeper means faster.
- Flat = no change; peaks/troughs = turning points.
- Multiple lines = compare several series at once.
Why connect the dots with lines instead of leaving them as a scatter of points?
Line graph vs scatter plot?
Line graph: one y for each x, x is ordered (usually time), points connected. Scatter plot: each point is an independent (x, y) pair, no connecting lines, used to spot correlation.
Don't connect dots when the x-axis is categories (apples, bananas, cherries). The 'line between apples and bananas' is meaningless. Use a bar graph.
Watch the axes: a 'dramatic crash' often shrinks to a wiggle once you start the y-axis at 0 and use a sensible time range.
- Line graphs show change over an ordered variable (usually time).
- Slope = rate of change; flat = steady.
- Only valid when the x-axis is continuous/ordered, not categorical.