Using regular labels as chart title

Normally, the chart titles are centered over plot area. If you need them centered over the whole chart area, you can use labels instead.

For that, use allLabels chart setting.

You may also need to use marginTop in order to give the label/title some space.

"allLabels": [{
  "text": "This is chart-area-centered label",
  "align": "center",
  "bold": true,
  "size": 20,
  "y": 10
}],
"marginTop": 50