Choropleth of unemployment rate per county

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  "width": 500,
  "height": 300,
  "data": {
    "url": "data/us-10m.json",
    "format": {
      "type": "topojson",
      "feature": "counties"
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  "transform": [{
    "lookup": "id",
    "from": {
      "data": {
        "url": "data/unemployment.tsv"
      },
      "key": "id",
      "fields": ["rate"]
    }
  }],
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  "encoding": {
    "color": {
      "field": "rate",
      "type": "quantitative"
    }
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