Change over time
Area chart
Emphasises magnitude by filling the region between a line and a baseline.
- Chart
- Trend over time
- Magnitude
What it answers
How large is the value across time?
- Shape
- Filled area below a line
- What it shows
- Sustained levels and large changes.
Example: Alta Sky Centre AS
The question
When in the season does Alta Sky Centre need its seasonal staff?
Alta Sky Centre seasonal staff by month, 2025
Alta Sky Centre AS is a fictional company created for Insyt.
The misleading version
Same question, drawn badly
Area chart with the baseline at 50
What goes wrong. The filled area starts at 50, not zero. October's 60 looks tiny next to 110, and April's 10 drops off the chart. An area chart must start at zero.
When to use it
Use it when
Emphasising magnitude in one nonnegative time series.
Avoid it when
When overlapping fills hide series or a truncated baseline misleads.
How to read it
Read the upper boundary as value; filled height shows distance from the baseline.
The data you need
- Layout
- Long table
- Fields
- Time: date/datetime or ordered number; Value: number
- One row is
- One observation at a time or ordered position. What is the grain?
- Rules
- Parse dates consistently and sort ascending. Resolve duplicate timestamps by a declared rule. Missing values are not automatically zero.
- Optional
- Optional Series. Use regular spacing for methods requiring it.
- Preparation
- Parse and sort timestamps or sequence positions; aggregate duplicates deliberately and preserve gaps. Parse dates consistently and sort ascending. Resolve duplicate timestamps by a declared rule. Missing values are not automatically zero.
- Units
- Time uses a stated date/time unit and sampling period; the value axis uses the measure's unit. Rates need their own explicit denominator.
Worked example
Data Jan 30, Feb 34, Mar 38. Fill from zero to the line. March is 8 units above January; area does not create an extra total.
| Time | Value |
|---|---|
| 2026-01-01 | 30 |
| 2026-02-01 | 34 |
| 2026-03-01 | 38 |