arc.outerRadius()

arc.outerRadius([radius])

If radius is specified, sets the outer radius to the specified function or number and returns this arc generator. If radius is not specified, returns the current outer radius accessor, which defaults to:

function outerRadius(d) {
  return d.outerRadius;
}

Specifying the outer radius as a function is useful for constructing a coxcomb or polar bar chart, often in conjunction with a sqrt scale. More commonly, a constant outer radius is used for a pie or donut chart. If the outer radius is smaller than the inner radius, the inner and outer radii are swapped. A negative value is treated as zero.