const pt = point([ 0, 1 ]);
const ptLength = length(pt); // 0
const line = lineString([ [ 0, 0 ], [ 1, 1 ] ]);
const lineLength = length(line); // 1.4142135623730951 = Math.sqrt(2)
const poly = polygon([ [ [ 1, 0 ], [ 2, 1 ], [ 3, 0 ], [ 1, 0 ] ] ]);
const polyLength = length(poly); // 4.82842712474619 = Math.sqrt(2) * 2 + 2