openlayers之点，线，面(以城市，河流，省份为例，分别对应点线面)

kpst._this这里指向初始化的map

     // 设置标注样式函数
    function createStyle(name) {
      // 河流style
      var riverStyle = new Style({
        stroke: new Stroke({
          color: '#4e89d4',
           2
        }),
        fill: new Fill({
          color: '#eee'
        })
      })
      // 省份style·
      var provinceStyle = new Style({
        stroke: new Stroke({
          color: '#4e89d4',
           1
        }),
        fill: new Fill({
          color: '#eee'
        })
      })

      //城市style·
      if (name != '') {
        var cityStyle = new ol.style.Style({
          image: new ol.style.Circle({
            radius: 5,
            fill: new ol.style.Fill({
              color: '#05ab57',
            }),
            stroke: new ol.style.Stroke({
              color: '#05ab57',
               1
            }),
          }),
          text: new ol.style.Text({
            textAlign: "center", // 位置
            textBaseline: "top", // 基准线
            font: "normal 12px 微软雅黑", // 文字样式
            text: name,
            fill: new ol.style.Fill({
              color: "#333",// 文本填充样式（即文字颜色)
            }),
            stroke: new ol.style.Stroke({
              color: "#Fff",
            }),
            zIndex: 9
          })
        })
      }
      return {
        riverStyle,
        provinceStyle,
        cityStyle
      }
    }
    //创建图层
    function creatlayer(name) {
      var layer
      if (name != 'city') {
        layer = new VectorLayer({
          name: name,
          source: new VectorSource({
            // 地图的坐标系是CGCS2000,json数据也要是CGCS2000
            features: (new GeoJSON()).readFeatures(require("../../assets/data/" + name + '.json'))
          }),
          style: createStyle()[name + 'Style']
        });

      } else {
        var features = (new GeoJSON()).readFeatures(require("../../assets/data/city.json"))
        for (let i = 0; i < features.length; i++) {
          const feature = features[i];
          feature.setStyle(createStyle(feature.get("NAME")).cityStyle)
        }
        layer = new VectorLayer({
          name: name,
          source: new VectorSource({
            features: features
          })
        })
      }
      kpst._this.addLayer(layer);
      return layer
    };
    // 将图层加载到地图，并将所加图层赋给地图的某个对象
    function layerFx(name) {
      kpst._this[name] = creatlayer(name)
    }
    // 将图层加载函数挂载到地图
    kpst._this.layerFx = layerFx