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Scatter Chart (Scatter)

easy-chart-lit · Manual

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Scatter Chart (Scatter)

This chapter explains the data field conventions for Scatter charts in EasyChart, especially the compatibility behavior of SeriesData.y/value, and how the z dimension drives sizeMapping.

1. Use cases

  • Correlation analysis (two numeric dimensions X/Y)
  • Distribution visualization (point cloud)
  • Outlier detection

2. Minimum viable setup (checklist)

  1. ChartProfile.coordinateSystem = Cartesian2D
  2. Axes
    • Common: X=Value, Y=Value
  3. Series
    • Add 1 Serie
    • Serie.type = Scatter
    • Serie.seriesData has at least 2 points

3. Inspector fields

  • series[i].type = Scatter
  • series[i].settings: actual type is ScatterSettings
    • point: point style (visible/size/texture)
    • hover: hover highlight (enabled/pickRadius/scale, etc. depending on version)
    • sizeMapping: point size mapping

4. SeriesData field interpretation (runtime behavior)

Scatter chart uses:

  • X coordinate: SeriesData.x
  • Y coordinate: prefers SeriesData.y
    • Compatibility: if y == 0 and value != 0, runtime uses value as y
  • Size mapping dimension: SeriesData.z (when sizeMapping.enabled=true)

So there are two common patterns:

  • x = X value
  • y = Y value

4.2 Compatibility (legacy data: use value as y)

  • x = X value
  • value = Y value
  • y = 0

Recommendation: for new data, write y directly to avoid mixing meanings with value.

5. Standard template: Value X + Value Y

  • X axis: AxisType = Value
  • Y axis: AxisType = Value
  • Data: use pattern 4.1 (x/y)

6. sizeMapping: actual behavior

When ScatterSettings.sizeMapping.enabled = true:

  • point radius is mapped from SeriesData.z
  • mapping range: minValue/maxValue -> minSize/maxSize
  • if clamp = true, t is clamped to 0..1
  • curve applies a curve transform to t (non-linear mapping)

If sizeMapping “doesn’t work”, check first:

  • did you actually set z values (default 0)
  • is minValue/maxValue equal (degenerates mapping)

7. Common pitfalls and troubleshooting

  • All points are on a horizontal line

    • you may have filled only value, but also set y to a non-zero value (compatibility won’t trigger)
    • recommend using y consistently as the Y coordinate

  • Hover does not respond

    • ScatterSettings.hover.enabled must be enabled
    • too small pickRadius makes picking difficult

  • Points are too small / too large

    • adjust ScatterSettings.point.size
    • or check minSize/maxSize in sizeMapping

8. Further reading

  • Axes/range, Series and data: 00_02-WorkflowAndLibrary.md
  • Common recipes: 04_08-CommonRecipes.md
  • FAQ: 04_09-FAQ.md