Tableau Course
Bar and Line Charts
Bar charts compare values across categories. Line charts show change over time. Together they cover the majority of business reporting needs — and mastering both in Tableau means controlling every visual detail from axis range to label position.
Bar Charts — The Right Tool for Comparisons
A bar chart encodes a Measure as the length of a rectangle. The longer the bar, the larger the value. This makes relative size instantly readable — the human eye compares bar lengths far more accurately than it compares angles (pie charts) or areas (bubble charts). Use a bar chart whenever your goal is to rank or compare values across a set of categories.
Bar Chart — Labelled Mockup
Axis Controls — Range, Title, and Gridlines
Double-clicking any axis opens the Edit Axis dialog. Here you can set a fixed range (useful when comparing charts with different scales), change the axis title, reverse the direction, or add a logarithmic scale. Right-clicking the axis gives additional options including Format (font, line style) and Add Reference Line. To remove gridlines, go to Format → Lines and set Grid Lines to None.
Line Charts — The Right Tool for Trends Over Time
A line chart connects data points with a line to show how a Measure changes over a continuous sequence — almost always time. The slope of the line encodes the rate of change: a steep upward slope means rapid growth, a flat line means no change, a downward slope means decline. Use a line chart whenever the sequence or direction of change is the story you want to tell.
Line Chart — Labelled Mockup
Discrete vs Continuous Dates on the Columns Shelf
The date pill colour tells you exactly how Tableau is treating the date field. A blue pill means discrete — the date is treated as a category label (e.g. "2022", "2023") and produces separate bars or points with gaps between them. A green pill means continuous — the date is treated as a numeric axis that flows without interruption. For line charts showing trends over time, always use a continuous (green) date pill so the line connects smoothly.
Bar vs Line — Choosing the Right Chart
| Scenario | Right chart | Reason |
|---|---|---|
| Comparing Sales across 17 product categories | Bar | Categories have no inherent order — bar length is the clearest comparison |
| Showing monthly revenue over 3 years | Line | Time is continuous and ordered — the slope tells the trend story |
| Comparing annual totals for 4 years | Bar | Only 4 data points — bar heights are clearer than a 4-point line |
| Tracking three KPIs each month over a year | Multi-line | Three coloured lines let you compare trend direction and magnitude simultaneously |
The most common beginner mistake with line charts is using a discrete date pill and wondering why the line looks like disconnected dots or separate vertical bars. Always check the pill colour before troubleshooting. Blue pill on a date field means Tableau is treating time as a category — right-click the pill, go to the lower section of the date options (the continuous ones), and select the level you need. Green pill means continuous — the line will connect. For bar charts, the most common mistake is forgetting to sort. An unsorted bar chart forces the reader to scan every bar to find the largest — sort descending and the story tells itself in the first two seconds.
Practice Questions
1. A line chart shows disconnected points instead of a smooth connected line. What colour is the date pill on the Columns shelf, and what does it need to be changed to?
2. You have a line chart of SUM(Sales) over time and want to split it into three separate lines — one per Category. What do you do?
3. Two bar charts need to be compared side by side but their axes have different ranges. How do you fix the axis range on one chart to match the other?
Quiz
1. You need to compare total Sales across 17 product Sub-Categories to find the top performers. Which chart type is most appropriate?
2. You want each bar in a horizontal bar chart to display its exact Sales value at the end of the bar. What do you do?
3. A line chart currently shows yearly data with a blue YEAR pill on the Columns shelf. You need it to show a monthly continuous trend instead. What do you do?
Next up — Lesson 22: Area and scatter charts — using filled areas to show cumulative volume and scatter plots to reveal correlation between two measures.