Charts

Line Chart

The easiest way to reveal trends and changes over time.

What is a line chart?

A line chart is designed to display information as a series of data points connected by straight line segments, making it excellent at showcasing trends in data over time. Typically, the x-axis represents the independent variable (often time), while the y-axis or dependent variable represents the values being measured. The individual data points are plotted on the graph, and the lines between them illustrate the progression or relationship between the variables.

This type of chart is particularly effective for identifying patterns, comparing datasets, and understanding growth or decline over time.

Line charts are versatile and can reveal trends with just a glance. This makes them one of the most popular and adaptable forms of data visualization.

Default line chart

A line chart that fully supports error visualization

Line chart showing the progression of two groups over time, with visual bands around each line representing their error margins.

First-class support for error visualization

It's important to provide an accurate image of the data by displaying any uncertainty. That's why Graphmatik line charts automatically calculate necessary summary statistics and support error visualization by default.

Graphmatik lets you customize your error visuals allowing you to plot area fills or error bars.

A line chart that visualizes error as area fills.

A line chart that shows error margins as error bars.

Y-axis: To cut or NOT to cut?

Cutting the y-axis, means setting the lower bound of the y-axis above zero. To say this is "SPICY drama" in the data vizualization community would be an understatement.

The argument against, rightly points out, that cutting the axis can exaggerate differences and potentially mislead viewers into perceiving larger changes than actually exist. While the argument for suggest time-series (line charts) are specifically designed to show trends and variations relative to a baseline and NOT absolute changes with respect to zero.

The concensus can best be summarized by Edward Tufte, an expert in data visualization.

“In general, in a time-series, use a baseline that shows the data not the zero point..." - Edward Tufte

Graphmatik's default behaviour is to cut the axis. Whether starting the y-axis at zero is appropriate for your data depends on the specific context of the data.

Line chart showing data over time. The y-axis starts at zero, which visually flattens the changes in the data.

Line chart showing data over time. The y-axis starts at the data's baseline and shows an upward trend overtime.

CAUTION: While cutting the axis of line charts is acceptable, it's bad practice for many other chart types, like bar charts, where the axis should always start at zero to accurately compare absolute differences.

Tips for creating beautiful line and area charts

Filtering

Leverage filters to highlight specific categories and make them instantly stand out.

Multi-series line chart showing various trends over time. One specific trend is highlighted in purple, with all other trends grayed out for comparison.

Uh-oh, Spaghetti-O

A "spaghetti plot" is a line chart with too many lines, making it hard to read. Aim for fewer than 5 lines per plot.

Multi-series line chart displaying a large number of trends over time, making individual trends difficult to distinguish.

A multi-series line chart clearly displaying three trends over time.

Chart properties

Prop	Default	Description
`central tendency`	mean	mean The sum of a set of values divided by the number of values in the set. median The middle most value of a sorted set of numbers.
`error`	SEM	standard error of the mean (SEM) `mean` How much the sample means vary from the population mean. standard deviation (SD) `mean` A measure of the variation of a set of values around their mean. 95% confidence interval (95% CI) `mean or median` 95% probability that the population parameter lies within this range. range `mean or median` The difference between the highest and lowest values within a set. Interquartile range (IQR) `median` The middle 50% of a set of values (i.e. 3rd quartile - 1st quartile).
`error format`	areas	areas Error shown as filled areas between dashed bounds. bars Visualize error as a set of upper and lower error bars.
`points`	all	all Show individual data points as dots. leading Show ONLY the leading data point as a dot. false Hide all individual data points.
`line`	linear	linear Data points are connected by straight line segments. curved Data points are connected by curved line segments. step before Staircase-like line segments. The y-value changes before the x-value. step after Staircase-like line segments. The y-value changes after the x-value.

Lollipop Chart

A simple, yet elegant alternative to the classic bar chart.

Area Chart

A bolder line chart designed to emphasize magnitude and cumulative totals.

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