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// A Single View or a Layer Specification
  "mark/layer": ...,
  "encoding": {     // Encoding
    ...: {
      "field": ..., // Field
      "type": "quantitative",

A field definition of an encoding channel must include a field in order to map an encoding channel to a data field. The sort field definition can also have the field property to sort the encoded field by another field as well.

The field property can be one of:

1) A string representing the data field.

For example, we can set field to "precipitation" to map it to x position.

Valid JavaScript object access paths using either dot (e.g., or bracket with quotes (e.g., foo['bar']) notations can be used in field to perform nested object lookups. If field names contain dots or brackets but are not nested, use \\ to escape dots and brackets. For example, if the field name is a.b, use a\\.b. Similarly, if the field name is a[0], use a\\[0\\].

Further note that in JSON, you have to escape backslashes. Hence, a single backslash (\) is escaped as \\\\ in JSON. You also need to escape quotes (\") and use special escape characters for newlines (\n), carriage returns (\r), and tabs (\t).

2) An object defining iterated values from the repeat operator

For example, we can set field of x channel to {"repeat": "column"} to create a histogram of different fields.

See the repeat page for more information about the repeat operator and more examples.