// Single View Specification
{
  "data": ... ,
  "mark": "errorband",
  "encoding": ... ,
  ...
}

Have you ever needed to visualize the uncertainty or variability within your quantitative data? This guide will show you how to do just that using error bands in Vega-Lite. An error band summarizes an error range of quantitative values by displaying them as a shaded area. You can either aggregate raw data or directly visualize aggregated data with error bands.

Quick Start: How to Create an Error Band

To create an error band, you simply set mark to "errorband" in your Vega-Lite specification.

{
  "data": { ... },
  "mark": "errorband",
  "encoding": { ... }
}

Why Use Error Bands?

Error bands are perfect for summarizing error ranges and displaying them visually. They help to provide a clear representation of variability or uncertainty within data sets, making your visualizations more informative.

Comparing Error Bands and Error Bars

While both error bands and error bars serve to display error ranges, error bands use shaded areas, which can be more visually comprehensive. For example, an error band visually smooths the data, making it easier to interpret compared to individual error bars.

Error Band Example:

Error Bar Example:

How to Use Error Bands

Aggregating Raw Data

When your data isn't aggregated yet, Vega-Lite can help with that. It will aggregate the data based on the extent properties defined in your mark. This is very handy when you want to display a confidence interval, for example.

Pre-Aggregated Data

Say your data is already aggregated and contains low and high values of the error band. You can directly specify x and x2 (or y and y2) in your encoding to use the error band as a ranged mark.

Alternatively, if your pre-aggregated data contains center and error values, you can use x/y, x/yError, and x/yError2 in your encoding.

Customizing Your Error Band

Different Parts of the Error Band

An error band is essentially a composite mark in Vega-Lite, made up of layered plots. This allows for extensive customization. For example, you can:

• Add borders and customize their properties like strokeDash and opacity
• Customize the color and opacity by using the corresponding encoding channels

"errorband": {
    "extent": "ci", 
    "band": {"color": "lightblue"},
    "borders": {"color": "blue", "strokeDash": [4, 4]}
}

Applying Color and Opacity

You can dynamically set the color and opacity of your error band to make it stand out.

"encoding": {
    "color": {"value": "black"},
    "opacity": {"value": 0.3}
}

Tooltip Customization

You can add custom tooltips to your error bands to provide additional information when users hover over them.

Common Questions About Error Bands

FAQ

Q: When should I use an error band instead of an error bar?

A: Use an error band when you want a smoother and more visually comprehensive representation of the variability in your data. Error bands can make it easier to interpret the overall trend and uncertainty.

Q: Can I customize the colors and opacity of my error band?

A: Absolutely! You can use the color and opacity encoding channels to make your error bands visually appealing and better suited to your data visualization needs.

Q: How do I add tooltips to my error bands?

A: You can add custom tooltips by specifying them in the encoding. This will override the default tooltips and provide more detailed information to users.

By following this guide, you'll be able to create informative and visually appealing error bands in Vega-Lite, making your data visualizations more effective in communicating uncertainty and variability. Happy visualizing!