Openlayers 4.3.1没有显示我的GeoJSON层

Question

Please i want to display a layer from GeoJSON file with openlayers 4.3.1 but the result (the vectorLayer variable) show a blank page. What am i missing?

The GeoJSON file is here https://gist.githubusercontent.com/abdounasser202/5d830738ad29e6395743530545bd322b/raw/0c34d9a1ced1879432318b6860c1c21e8e88ef04/quartiers_yaounde.geojson

Here is my JS code

    var styles = {
   'Polygon': new ol.style.Style({
     stroke: new ol.style.Stroke({
       color: 'grey',
       width: 1
     }),
     fill: new ol.style.Fill({
       color: 'rgba(0, 0, 255, 0.1)'
     })
   }),
  };

  var styleFunction = function(feature) {
   return styles[feature.getGeometry().getType()];
  };

  var geojsonObject = 'https://gist.githubusercontent.com/abdounasser202/5d830738ad29e6395743530545bd322b/raw/0c34d9a1ced1879432318b6860c1c21e8e88ef04/quartiers_yaounde.geojson';
  console.log("geodata >>> ", geojsonObject);

  var vectorSource = new ol.source.Vector({
        format: new ol.format.GeoJSON(),
        url: geojsonObject
    });

  var vectorLayer = new ol.layer.Vector({
    source: vectorSource,
    style: styleFunction
  });

  var raster = new ol.layer.Tile({
    source: new ol.source.OSM()
  });

  // var extent_degree = [11.4095, 3.71349, 11.5747, 3.9692];

  var map = new ol.Map({
   layers: [vectorLayer],
   target: 'map',
   view: new ol.View({
      // projection: 'EPSG:4326',
      center: ol.proj.fromLonLat([11.5021, 3.8480]),
      zoom: 6
   })
  });

  // ol.proj.get('EPSG:4326').setExtent(extent_degree)

  var units = map.getView().getProjection().getUnits();
  console.log("units >>> ", units);

  var projections = map.getView().getProjection();
  console.log("projections >>> ", projections);

Answer 1

According your code, you are styling Polygons, but no other geometry types. So you will see only Polygons on your map. Other geometry types will be invisible since they are not styled. The GeoJSON file does not contain Polygons, so indeed you won't see anything.

As far as I can see, the GeoJSON file contains only MultiPolygons. To make them visible, add a style for 'MultiPolygon' in the variable styles, or just change the string 'Polygon' in your code to 'MultiPolygon'.