Cool special effects in WebGIS administrative area - streamer special effects tutorial

First look at the effect:

 

Picture screenshot:

The idea of ​​​​the streamer special effect is to replace several lines from the boundary of the administrative area with another highlight color over time.

The first step of streamer is to shine, and the tutorial of glowing is here:

GIS vector graphics polygonal plot administrative area glow, shadow glow special effect realization_Crazy GISer's Blog-CSDN Blog

After learning to emit light, the next thing to do is to make the graphics "move" on the basis of emitting light. In fact, the boundary of a graph is an array of latitude and longitude, we can use this array to do some articles.

Conventionally, the data of a polygon looks like this:
 

{
  type: "FeatureCollection",
  features: [
    {
      type: "Feature",
      properties: {
        adcode: 341000,
        name: "黄山市",
        center: [118.317325, 29.709239],
        centroid: [118.0