Aggregate Bar Chart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "description": "A bar chart showing the US population distribution of age groups in 2000.",
  "data": { "url": "data/population.json"},
  "transform": [{"filter": "datum.year == 2000"}],
  "mark": "bar",
  "encoding": {
    "y": {
      "field": "age", "type": "ordinal",
      "scale": {"rangeStep": 17}
    },
    "x": {
      "aggregate": "sum", "field": "people", "type": "quantitative",
      "axis": {"title": "population"}
    }
  }
}