Book Image

Mastering OpenLayers 3

By : Gábor Farkas
Book Image

Mastering OpenLayers 3

By: Gábor Farkas

Overview of this book

OpenLayers 3 allows you to create stunning web mapping and WebGIS applications. It uses modern, cutting edge browser technologies. It is written with Closure Library, enabling you to build browser-independent applications without painful debugging ceremonies, which even have some limited fallback options for older browsers. With this guide, you will be introduced to the world of advanced web mapping and WebGIS. First, you will be introduced to the advanced features and functionalities available in OpenLayers 3. Next, you will be taken through the key points of creating custom applications with OpenLayers 3. You will then learn how to create the web mapping application of yours (or your company's) dream with this open source, expense-free, yet very powerful library. We’ll also show you how to make amazing looking thematic maps and create great effects with canvas manipulation. By the end of this book, you will have a strong command of web mapping and will be well on your way to creating amazing applications using OpenLayers 3.
Table of Contents (17 chapters)
Mastering OpenLayers 3
Credits
About the Author
About the Reviewer
www.PacktPub.com
Preface
Index

Accessing attributes


In the first example (ch04_getattribute), we will learn how to access attribute data stored in the features and communicate them to the user. We will use a very particular feature of OpenLayers 3: the overlay. As a first step, we will create some simple rules to be applied on our overlays:

.popup {
    border: 1px solid grey;
    background-color: rgba(255,255,255,1);
    border-radius: .5em;
}

Note

Overlays are geographically bounded HTML elements, which scale with the current resolution. They are stored separately from layers and other elements of the library, allowing us to have full control over them. As they are not parts of the canvas, we can easily style them with CSS.

Writing the code

For this task, we simply register a click event to our map, querying the underlying vector layers:

map.on('click', function (evt) {
    var pixel = evt.pixel;
    var coord = evt.coordinate;
    var attributeDiv = document.createElement('div');
    attributeDiv.className = 'popup';
 ...