var params = {
  "options": {
    "scales": {
      "Sepal.Length": {
        "sync": [true]
      },
      "Sepal.Width": {
        "sync": [true]
      },
      "Species": {
        "sync": [false]
      }
    }
  }
} 

var facet = {
  "type": ["rect"],
  "opts": {
    "fields": ["Species"],
    "autoSetAxis": [true]
  },
  "geoms": [
    {
      "type": ["point"],
      "position": ["Sepal.Length*Sepal.Width"],
      "color": ["Species"]

    }
  ]
}