Line drawn between airports in the U.S. simulating a flight itinerary

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "description": "Line drawn between airports in the U.S. simulating a flight itinerary",
  "width": 800,
  "height": 500,
  "layer": [
    {
      "data": {
        "url": "data/us-10m.json",
        "format": {
          "type": "topojson",
          "feature": "states"
        }
      },
      "projection": {
        "type": "albersUsa"
      },
      "mark": {
        "type": "geoshape",
        "fill": "#eee",
        "stroke": "white"
      }
    },
    {
      "data": {
        "url": "data/airports.csv"
      },
      "projection": {
        "type": "albersUsa"
      },
      "mark": "circle",
      "encoding": {
        "longitude": {
          "field": "longitude",
          "type": "quantitative"
        },
        "latitude": {
          "field": "latitude",
          "type": "quantitative"
        },
        "size": {
          "value": 5
        },
        "color": {
          "value": "gray"
        }
      }
    },
    {
      "data": {
        "values": [
          {"airport": "SEA", "order": 1},
          {"airport": "SFO", "order": 2},
          {"airport": "LAX", "order": 3},
          {"airport": "LAS", "order": 4},
          {"airport": "DFW", "order": 5},
          {"airport": "DEN", "order": 6},
          {"airport": "ORD", "order": 7},
          {"airport": "JFK", "order": 8}
        ]
      },
      "transform": [
        {
          "lookup": "airport",
          "from": {
            "data": {
              "url": "data/airports.csv"
            },
            "key": "iata",
            "fields": [
              "latitude",
              "longitude"
            ]
          }
        }
      ],
      "projection": {
        "type": "albersUsa"
      },
      "mark": "line",
      "encoding": {
        "longitude": {
          "field": "longitude",
          "type": "quantitative"
        },
        "latitude": {
          "field": "latitude",
          "type": "quantitative"
        },
        "order": {
          "field": "order",
          "type": "ordinal"
        }
      }
    }
  ]
}