Line series: the path itself

An arc derives the great circle between two endpoints. A line series is the opposite contract: you supply the vertex sequence and it is drawn in order, which is what a sea lane, a GPS trace, an expedition or a pipeline actually is. Rendering still runs through the projection, so a route crossing the antimeridian is cut at the map edge rather than streaking backwards, and segments between vertices follow the sphere. Hover a route for its name and value.

The configuration

value drives width through the same size-scale machinery bubbles use, per-datum color overrides the series colour, and endpoints marks each terminus with a screen-space dot that does not grow when the reader zooms.

{
  type: 'line',
  name: 'Trade routes',
  data: [{
    name: 'Europe – East Asia (sea)',
    path: [[-0.1, 51.5], [-5.6, 36.0], [32.3, 31.3], ...],
    value: 100,
  }],
  width: { range: [1, 5] },
  endpoints: { show: true, radius: 2.5 },
}