6. Specify Visual Encodings
Visual encodings specify how values in a data field is mapped to properties of a visual channel. To specify a visual encoding, we need an example mark/glyph/collection, a data field, and a visual channel:
scene.encode(rect, {field: "Percentage", channel: "width"});
Atlas will automatically create a scale based on the provided parameters, the type and value distribution of the data field, and the type and current values of the visual channel.
Scale Type
The following describes the heuristics for automatically choosing the scale type based on an encoding specification:
| field type | channel | scale type |
|---|---|---|
| integer or number | “width”, “height”, “x”, “y”, “angle”, “radialDistance”, “radius” | linear |
| date | “width”, “height”, “x”, “y”, “radialDistance”, “radius” | time |
| string | “x”, “y” | point |
| integer or number | “fillColor”, “strokeColor” | sequentialColor |
| string | “fillColor”, “strokeColor” | ordinalColor |
For “log” and “power” scale types, you can specify them as the “scaleType” parameter in the encode method.