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Leaflet JS: Resizing a map to keep a circle diameter inside it

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Leaflet JS: Resizing a map to keep a circle diameter inside it

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I’ve been working on creating a UI to make searching for the football stadiums that I wrote about last week a bit easier and I thought I’d give Leaflet JS a try.

Leaflet is a Javascript library which was recommended to me by Jason Neylon) and can be used as a wrapper around Open Street Map.

I started by creating a simple form where you could fill in a lat/long and distance and it would centre the map on that lat/long and show you a list of the stadiums within that diameter next to the map.

Having done that I wanted to draw the diameter onto the map and then show the location of the stadiums which fitted inside the circle.

I had the following code to centre the map and draw a circle:

  var distance = 10;
  $("#inputDistance").val(distance);
  var latLong=[51.505, -0.11398315429687499];
  $("#inputLatLong").val(latLong)
 
  var map = L.map('map').setView(latLong,11);
  var layer = L.tileLayer('http://{s}.tile.cloudmade.com/e7b61e61295a44a5b319ca0bd3150890/997/256/{z}/{x}/{y}.png', { maxZoom: 18 });
  layer.addTo(map);
 
  var currentDiameter = L.circle(latLong, distance * 1000);
  currentDiameter.addTo(map);
 
  var currentPositionMarker = L.marker([latLong[0], latLong[1]]);
  currentPositionMarker.addTo(map);

which creates this map:

Map

I wanted to be able to change the diameter of the circle from the form and have it pick up more stadiums which I did with the following code:

  $("#inputDistance").change(function() {	
    map.removeLayer(currentDiameter);
    currentDiameter = L.circle(currentPositionMarker.getLatLng(), $("#inputDistance").val() * 1000);
    currentDiameter.addTo(map);
  });

I updated the diameter to be 16km and the map looked like this:

Map diameter

It just about fits inside the map but setting it to anything higher means that the area of the diameter falls outside of the visible map which is annoying.

I wanted to be able to resize the map when the circle changed in size and after a bit of browsing of the Leaflet code I came across a function called ‘fitBounds’ which lets us achieve this. I changed the code like so:

  $("#inputDistance").change(function() {	
    map.removeLayer(currentDiameter);
    currentDiameter = L.circle(currentPositionMarker.getLatLng(), $("#inputDistance").val() * 1000);
    currentDiameter.addTo(map);
    map.fitBounds(currentDiameter.getBounds());
  });

Now if I change the distance the map resizes too:

Map diameter fixed

Much better!

The full code to do this reads like so:

$(document).ready(function() {		
  var distance = 10;
  $("#inputDistance").val(distance);
  var latLong=[51.505, -0.11398315429687499];
  $("#inputLatLong").val(latLong)
 
  var map = L.map('map').setView(latLong,11);
  var layer = L.tileLayer('http://{s}.tile.cloudmade.com/e7b61e61295a44a5b319ca0bd3150890/997/256/{z}/{x}/{y}.png', { maxZoom: 18 });
  layer.addTo(map);
 
  var currentDiameter = L.circle(latLong, distance * 1000);
  currentDiameter.addTo(map);
 
  var currentPositionMarker = L.marker([latLong[0], latLong[1]]);
  currentPositionMarker.addTo(map);
 
  $("#inputDistance").change(function() {	
    map.removeLayer(currentDiameter);
    currentDiameter = L.circle(currentPositionMarker.getLatLng(), $("#inputDistance").val() * 1000);
    currentDiameter.addTo(map);
    map.fitBounds(currentDiameter.getBounds());
  }); 
});

The code for this is all on github although I’ve refactored it a bit now so it doesn’t look exactly like this. I tried to put it on jsfiddle as well but it didn’t seem to work very well so screenshots it is!

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Published at DZone with permission of Mark Needham, DZone MVB. See the original article here.

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