Leaflet Quickstart

Leaflet on JavaScript-kirjasto selainpohjaisia, mobiiliystävällisiä, interaktiivisia karttoja varten. Se on kevyt, mutta sisältää kuutenkin suurimman osan ominaisuuksista, joita kehittäjä tarvitsee online-karttoihin. Leafletiä suunnitellessa yksinkertaisuus, suorituskyky ja käytettävyys on pidetty mielessä.

Sisältö

• Leaflet Quickstart

  • Suorittaminen

  • Sivun valmistelu

  • Setting up the Map

  • Merkit, ympyrät ja polygonit

  • Työskentely ponnahdusikkunoiden kanssa

  • Tapahtumien käsittely

  • Mitä seuraavaksi?

Suorittaminen

Prior to running this quick start you should start MapProxy. On OSGeoLive this can be found under Geospatial\Web Services\MapProxy\Start MapProxy. This will provide background tiles that will be used in this demo.

Katso esimerkki

Vihje

If you are reading this quickstart outside OSGeoLive you may prefer reading the original demo on: https://leafletjs.com/examples/quick-start/, since this demo uses tilestache on OSGeoLive.

Sivun valmistelu

Before writing any code for the map, you need to do the following preparation steps on your page:

• Include Leaflet CSS files in the head section of your document

<link rel="stylesheet" href="/leaflet/leaflet.css" />

• Ota mukaan Leaflet JavaScript-tiedosto:

<script src="/leaflet/leaflet.js"></script>

• aseta div elementti tietyn id:n kanssa kohtaan, jossa haluat kartan sijaitsevan:

<div id="map"></div>

• Make sure the map container has a defined height, for example by setting it in CSS:

#map { height: 180px; }

Now you are ready to initialize the map and do some stuff with it.

Setting up the Map

Let’s create a map of Firenze, Italy with an indication of the 2022 FOSS4G conference. First we’ll initialize the map and set its view to our chosen geographical coordinates and a zoom level:

var map = L.map('map').setView([43.77913, 11.24938], 15);

By default (as we didn’t pass any options when creating the map instance), all mouse and touch interactions on the map are enabled, and it has zoom and attribution controls.

Note that setView call also returns the map object - most Leaflet methods act like this when they don’t return an explicit value, which allows convenient jQuery-like method chaining.

Next we’ll add a tile layer to our map. In this case we will be using the tile images provided by MapProxy on the live dvd. Note that using nicer background maps such as openstreetmap will result in a much better user experience.

Creating a tile layer usually involves setting the URL template for the tile images, the attribution text and the maximum zoom level of the layer:

L.tileLayer('http://localhost:8011/wmts/mapnik_tile/GLOBAL_WEBMERCATOR/{z}/{x}/{y}.png',{}).addTo(map);

If you have online access you may want to use a nicer tilemap as the background:

L.tileLayer('http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png',{maxZoom:18, attribution: '© <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'}).addTo(map);

Make sure all the code is called after the div and leaflet.js inclusion. That’s it! You have a working Leaflet map now.

It’s worth noting that Leaflet is provider-agnostic, meaning that it doesn’t enforce a particular choice of providers for tiles, and it doesn’t even contain a single provider-specific line of code, so you’re free to use other providers if you need to.

Merkit, ympyrät ja polygonit

Besides tile layers, you can easily add other things to your map, including markers, polylines, polygons, circles and popups. Let’s add a marker:

var marker = L.marker([43.77913, 11.24938]).addTo(map);

Adding a circle is the same (except for specifying the radius in meters as a second argument), but lets you control how it looks by passing options as the last argument when creating the object:

var circle = L.circle([43.777, 11.255], 250, {
   color: 'red',
   fillColor: '#f03',
   fillOpacity: 0.5
}).addTo(map);

Polygonin lisääminen on yhtä helppoa:

var polygon = L.polygon([
    [43.775, 11.247],
    [43.784, 11.240],
    [43.778, 11.238]
]).addTo(map);

Työskentely ponnahdusikkunoiden kanssa

Ponnahdusikkunoita käytetään yleensä kun halutaan yhdistää tietoa johonkin kohteeseen kartalla. Leafletissä on todella kätevä oikotie tätä varten:

var popup = L.popup()
   .setLatLng([43.77913, 11.24938])
   .setContent("FOSS4G is here this year!")
   .openOn(map);

Here we use openOn instead of addTo because it handles automatic closing of a previously opened popup when opening a new one which is good for usability.

Tapahtumien käsittely

Every time something happens in Leaflet, e.g. user clicks on a marker or map zoom changes, the corresponding object sends an event which you can subscribe to with a function. It allows you to react to user interaction:

function onMapClick(e) {
   alert("You clicked the map at " + e.latlng);
}

map.on('click', onMapClick);

Each object has its own set of events - see documentation for details. The first argument of the listener function is an event object - it contains useful information about the event that happened. For example, map click event object (e in the example above) has latlng property which is a location at which the click occured.

Let’s improve our example by using a popup instead of an alert:

var popup = L.popup();

function onMapClick(e) {
   popup
        .setLatLng(e.latlng)
        .setContent("You clicked the map at " + e.latlng.toString())
         .openOn(map);
}

map.on('click', onMapClick);

Kokeile klikata karttaa niin näet koordinaatit ponnahdusikkunassa. Katso täydellinen esimerkki

Mitä seuraavaksi?

Nyt olet oppinut Leafletin perusteet ja voit aloittaa rakentamaan karttasovelluksia saman tien! Muista katsoa myös yksityiskohtaista dokumentaatiota ja muita esimerkkejä.