Append Layer to overlayMaps in Leaflet

What if we want to create a layer based on geolocation, but have the layer only be added to the map once geolocation occurs? I didn't find this example in any Leaflet tutorials, but it's pretty simple with some basic JavaScript

I'll start with some code that should look familiar from the Leaflet Quick Start Guide, but with each item as its own layer.

  var marker = L.marker([51.5, -0.09]);

  var circle = L.circle([51.508, -0.11], 500, {
      color: 'red',
      fillColor: '#f03',
      fillOpacity: 0.5
  });

  var polygon = L.polygon([
      [51.509, -0.08],
      [51.503, -0.06],
      [51.51, -0.047]
  ]);

  var map = L.map('map', {
    center: [51.505, -0.09],
    zoom: 13,
    layers: [marker, circle, polygon]
  });

  var overlayMaps = {
    "Marker": marker,
    "Circle": circle,
    "Polygon": polygon
  };
  L.tileLayer('http://tile.cloudmade.com/[API-KEY]/29889/256/{z}/{x}/{y}.png', {
    attribution: 'Map data &copy; <a href="http://openstreetmap.org">OpenStreetMap</a> contributors, <a href="http://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>, Imagery © <a href="http://cloudmade.com">CloudMade</a>',
    maxZoom: 18
  }).addTo(map);

Next let's add the code that will display the three original layers if geolocation does not occur. In this case, we do not want the geolocated layer to show.

  function onLocationError(e) {
    alert(e.message);

    L.control.layers(null, overlayMaps).addTo(map);
  }

  map.on('locationerror', onLocationError);

You can see in the below screenshot that only the three layers are displayed.

With Geolocation Off

Finally, we need to add code that will display all the layers (including the geolocation layer) if geolocation does occur. We simply need to add the "yourLocation" layer to overlayMaps and then display the layers as normal.

  function onLocationFound(e) {
    yourLocation = L.marker(e.latlng);

    overlayMaps["You"] = yourLocation;

    L.control.layers(null, overlayMaps).addTo(map);
  }

  map.on('locationfound', onLocationFound);

The screenshots below show what happens once geolocation has occurred.

With Geolocation On

Showing Geolocation Layer

 The full code is available in a gist.

References

• http://stackoverflow.com/questions/695050/how-do-i-add-a-property-to-a-javascript-object-using-a-variable-as-the-name

Add and Remove Leaflet Circle on Click

Similar to the popup example in the Leaflet tutorial, you might want to allow a user to add a circle centered on the point they click.

After defining your map, you first need to declare the variable you'll be using:

  var clickCircle;

While popups automatically disappear on the next click, circles do not. The following code removes the former circle from the leaflet map before drawing the new circle:

  function onMapClick(e) {
    if (clickCircle != undefined) {
      map.removeLayer(clickCircle);
    };

Next, we want our function to draw the new circle (NB: "1609 * 3" is the radius of the circle. This makes the radius equal 3 miles):

    clickCircle = L.circle(e.latlng, 1609 * 3, {
      color: '#f07300',
      fillOpacity: 0,
      opacity: 0.5
    }).addTo(map);
  }

And finally, we need to add an event listener so that the function will be run when a user clicks on the map:

  map.on('click', onMapClick);

The full code is available in a gist.

References

• http://leafletjs.com/examples/quick-start.html
• http://stackoverflow.com/questions/15507737/adding-removing-l-control-from-leaflet-js-map
• http://stackoverflow.com/questions/11272552/remove-polygon-from-the-map

Embed Audio in Leaflet Pop-up

Here's how to embed audio in a leaflet map. This example will also show you how to embed most other HTML in a leaflet map, or how to embed audio in an HTML file.

In the html file:

  function onEachAudio(feature, layer) {
    layer.bindPopup(feature.properties.name + "<br>" + feature.properties.html);
  };

  new L.GeoJSON.AJAX("audio.geojson", {
    onEachFeature: onEachAudio,
    pointToLayer: function(feature, latlng) {
      return L.marker(latlng, {icon: audioIcon});
    }
  }).addTo(map);

And here's the geojson format where you'll include your audio HTML and the coordinates where you want to view each file:

{
  "type": "FeatureCollection",
  "features": [
  {
    "type": "Feature",
    "properties": {
      "name": "<a href='http://www.freesound.org/people/genghis%20attenborough/sounds/212798/'>Deep basement</a>",
      "html": "<p><audio width='300' height='32' src='http://www.freesound.org/data/previews/212/212798_205108-lq.mp3' controls='controls'><br />Your browser does not support the audio element.<br /></audio></p>"
    },
    "geometry": {
      "type": "Point",
      "coordinates": [-100,34]
    }
  },{
    "type": "Feature",
    "properties": {
      "name": "<a href='http://www.freesound.org/people/John%20Sipos/sounds/125696/'>Atlantis docks then lands.</a>",
      "html": "<p><audio width='300' height='32' src='http://www.freesound.org/data/previews/125/125696_593024-lq.mp3' controls='controls'><br />Your browser does not support the audio element.<br /></audio></p>"
    },
    "geometry": {
      "type": "Point",
      "coordinates": [-84,40]
    }
  }
  ]
}

Just substitute in the address of your audio files for the sample files above in the "html" property of the geojson features.

Example Leaflet Map with Audio

The full code is available in a gist.

Import JSON Data from an External File in Leaflet

If your JSON or GeoJSON data is long, you might want to store it in a separate file to make your code more readable or to reduce repetition and allow you to access the same data file from multiple pages. You can do that with jQuery.

First, load jQuery 1.10.2 or the newest version of jQuery (2.0 onward does not support Internet Explorer 6, 7, or 8) in the header:

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>

Next, in your leaflet script at the bottom of the body, you'll need to add all your other code and your basemap, like normal, for example:

  var map = L.map('map').setView([38.0740, -55], 3);

  function onEachFeature(feature, layer) {
    layer.bindPopup(feature.properties.City + ", " + feature.properties.State + ", " + feature.properties.Country);
  }

Then, you can just use jQuery to get the JSON or GeoJSON file. A simple version of this would be:

  $.getJSON("cities.geoJSON", function (cities) {
    L.geoJson(cities).addTo(map);
  })

But you can also add more options to your L.geoJson code, just like you would if using data stored in the HTML file. For example:

  $.getJSON("cities.geoJSON", function (cities) {
    L.geoJson(cities, {
      onEachFeature: onEachFeature,
      pointToLayer: function (feature, latlng) {
        switch (feature.properties.Remember) {
          case '1': return L.marker(latlng, {icon: visitedIcon});
          case '?': return L.marker(latlng, {icon: uncertainIcon});
          case '0': return L.marker(latlng, {icon: uncertainIcon});
        }
      }
    }).addTo(map);
  })

So just a couple lines of jQuery allow you to store your JSON or GeoJSON data in a separate file.

The example code is available in a gist and the example is viewable here.

Further Reading

• http://lyzidiamond.com/posts/external-geojson-and-leaflet-the-other-way/