{
  "$schema": "urn:prism:schema:v1:spec",
  "title": "Arc primitive",
  "data": {
    "name": "arc_data",
    "values": [
      {"slice": "a", "weight": 1},
      {"slice": "b", "weight": 2},
      {"slice": "c", "weight": 3}
    ]
  },
  "mark": {"type": "arc"},
  "encoding": {
    "theta":  {"field": "weight", "type": "quantitative"},
    "color":  {"field": "slice",  "type": "nominal"},
    "radius": {"value": 80}
  }
}