Earthquakes in KML

Demonstrates the use of a Shape symbolizer to render earthquake locations.

This example parses a KML file and renders the features as a vector layer. The layer is given a style that renders earthquake locations with a size relative to their magnitude.

main.js

import KML from 'ol/format/KML.js';
import Map from 'ol/Map.js';
import StadiaMaps from 'ol/source/StadiaMaps.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';
import {Circle as CircleStyle, Fill, Stroke, Style} from 'ol/style.js';
import {Tile as TileLayer, Vector as VectorLayer} from 'ol/layer.js';

const styleCache = {};
const styleFunction = function (feature) {
  // 2012_Earthquakes_Mag5.kml stores the magnitude of each earthquake in a
  // standards-violating <magnitude> tag in each Placemark.  We extract it from
  // the Placemark's name instead.
  const name = feature.get('name');
  const magnitude = parseFloat(name.substr(2));
  const radius = 5 + 20 * (magnitude - 5);
  let style = styleCache[radius];
  if (!style) {
    style = new Style({
      image: new CircleStyle({
        radius: radius,
        fill: new Fill({
          color: 'rgba(255, 153, 0, 0.4)',
        }),
        stroke: new Stroke({
          color: 'rgba(255, 204, 0, 0.2)',
          width: 1,
        }),
      }),
    });
    styleCache[radius] = style;
  }
  return style;
};

const vector = new VectorLayer({
  source: new VectorSource({
    url: 'data/kml/2012_Earthquakes_Mag5.kml',
    format: new KML({
      extractStyles: false,
    }),
  }),
  style: styleFunction,
});

const raster = new TileLayer({
  source: new StadiaMaps({
    layer: 'stamen_toner',
  }),
});

const map = new Map({
  layers: [raster, vector],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

const info = document.getElementById('info');
info.style.pointerEvents = 'none';
const tooltip = new bootstrap.Tooltip(info, {
  animation: false,
  customClass: 'pe-none',
  offset: [0, 5],
  title: '-',
  trigger: 'manual',
});

let currentFeature;
const displayFeatureInfo = function (pixel, target) {
  const feature = target.closest('.ol-control')
    ? undefined
    : map.forEachFeatureAtPixel(pixel, function (feature) {
        return feature;
      });
  if (feature) {
    info.style.left = pixel[0] + 'px';
    info.style.top = pixel[1] + 'px';
    if (feature !== currentFeature) {
      tooltip.setContent({'.tooltip-inner': feature.get('name')});
    }
    if (currentFeature) {
      tooltip.update();
    } else {
      tooltip.show();
    }
  } else {
    tooltip.hide();
  }
  currentFeature = feature;
};

map.on('pointermove', function (evt) {
  if (evt.dragging) {
    tooltip.hide();
    currentFeature = undefined;
    return;
  }
  const pixel = map.getEventPixel(evt.originalEvent);
  displayFeatureInfo(pixel, evt.originalEvent.target);
});

map.on('click', function (evt) {
  displayFeatureInfo(evt.pixel, evt.originalEvent.target);
});

map.getTargetElement().addEventListener('pointerleave', function () {
  tooltip.hide();
  currentFeature = undefined;
});

index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <title>Earthquakes in KML</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css">
    <link rel="stylesheet" href="node_modules/ol/ol.css">
    <style>
      .map {
        width: 100%;
        height: 400px;
      }
      #map {
        position: relative;
      }
      #info {
        position: absolute;
        height: 1px;
        width: 1px;
        z-index: 100;
      }
      .tooltip.in {
        opacity: 1;
      }
      .tooltip.top .tooltip-arrow {
        border-top-color: white;
      }
      .tooltip-inner {
        border: 2px solid white;
      }
    </style>
  </head>
  <body>
    <div id="map" class="map">
      <div id="info"></div>
    </div>

    <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js"></script>
    <script type="module" src="main.js"></script>
  </body>
</html>

package.json

{
  "name": "kml-earthquakes",
  "dependencies": {
    "ol": "9.1.0"
  },
  "devDependencies": {
    "vite": "^3.2.3"
  },
  "scripts": {
    "start": "vite",
    "build": "vite build"
  }
}