How to Resolve Scale and Guide Issues in Vega-Lite?

When creating data visualizations with Vega-Lite, you might wonder how to manage the resolution of scales, axes, and legends, especially when dealing with multiple views. Let's walk you through this process in an easy and engaging way, so you can make better visualizations!

Understanding Scale and Guide Resolution

Vega-Lite determines whether scale domains (the input values for a scale) should be combined into a single scale. If scales are combined, their axes and legends might be merged as well. Otherwise, they will remain independent.

Here's the basic structure of the resolve property in Vega-Lite:

{
  "resolve": {
    "scale": {
      "CHANNEL": ...
    },
    "axis": {
      "POSITION_CHANNEL": ...
    },
    "legend": {
      "NON_POSITION_CHANNEL": ...
    }
  }
}

The resolve property can manage different aspects:

• Scale: Specifies how scales for each channel should be resolved.
• Axis: Defines how axes for positional channels (x and y) are resolved.
• Legend: Determines the resolution for non-positional channels (color, opacity, shape, size).

Each of these resolutions can be either "shared" or "independent". Independent scales imply separate axes and legends.

Example: Independent Color Scales in Repeated Charts

Imagine you have a visualization where you want to repeat the same chart but with different data subsets. You might want each chart to have its independent color scale. Here’s how you can set this up:

{
  "resolve": {
    "scale": {
      "color": "independent"
    }
  }
}

In this example, by setting the color scale to "independent", Vega-Lite automatically creates separate legends for each chart, ensuring clarity and precision in your data visualization.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "repeat": ["A", "B"],
  "spec": {
    "data": {
      "url": "data/cars.json"
    },
    "mark": "point",
    "encoding": {
      "x": {"field": "Horsepower", "type": "quantitative"},
      "y": {"field": "Miles_per_Gallon", "type": "quantitative"},
      "color": {"field": "Origin", "type": "nominal"}
    }
  },
  "resolve": {
    "scale": {
      "color": "independent"
    }
  }
}

FAQs

1. What does "shared" scale resolution mean in Vega-Lite?

• A "shared" scale resolution means that multiple views will share the same scale domain, resulting in synchronized axes or legends. For example, if two charts are set to share a color scale, they will use the same range of colors for their data points.

2. How can I make axes for x and y channels independent in a layered chart?

• You can set the axis resolution for x and y channels to "independent" within the resolve property:

  {
    "resolve": {
      "axis": {
        "x": "independent",
        "y": "independent"
      }
    }
  }

3. Is it possible to have independent legends for different data attributes in one chart?

• Yes, you can specify independent legends for different attributes by setting the legend property within resolve to "independent" for specific channels like color, size, etc.

  {
    "resolve": {
      "legend": {
        "color": "independent",
        "size": "independent"
      }
    }
  }

By understanding and utilizing the resolve property, you can enhance your Vega-Lite visualizations, making them more precise and easier to interpret. Happy visualizing!