flying indicates to a chart that you want to apply the JBJ actions of the said flyingFields to the data elements returned by the operator.

Often, the operator will return a JSON page containing at least:

{

  "recordsTotal": 108,
  "recordsFiltered": 108,
  "data": [
    {
      "_id": "Albania",
      "value": 2
    },
    {
      "_id": "Algeria",
      "value": 15
    }
  ]
}

If you declared a flyingFields like:

    "$country2iso": {
      "$_id": {
        "get": "_id",
        "mapping": {
          "Albania": "ALB",
          "Algeria": "DZA"
        }
      },
      "mask": "_id,value"
    }

and added a flying key to the chart, and its value was country2iso, then the data projected to the chart will be the previous data, treated by country2iso:

{

  "recordsTotal": 108,
  "recordsFiltered": 108,
  "data": [
    {
      "_id": "ALB",
      "value": 2
    },
    {
      "_id": "DZA",
      "value": 15
    }
  ]
}