Book Image

Learning D3.js 5 Mapping - Second Edition

By : Thomas Newton, Oscar Villarreal, Lars Verspohl
Book Image

Learning D3.js 5 Mapping - Second Edition

By: Thomas Newton, Oscar Villarreal, Lars Verspohl

Overview of this book

D3.js is a visualization library used for the creation and control of dynamic and interactive graphical forms. It is a library used to manipulate HTML and SVG documents as well as the Canvas element based on data. Using D3.js, developers can create interactive maps for the web, that look and feel beautiful. This book will show you how build and design maps with D3.js and gives you great insight into projections, colors, and the most appropriate types of map. The book begins by helping you set up all the tools necessary to build visualizations and maps. Then it covers obtaining geographic data, modifying it to your specific needs, visualizing it with augmented data using D3.js. It will further show you how to draw and map with the Canvas API and how to publish your visualization. By the end of this book, you'll be creating maps like the election maps and the kind of infographics you'll find on sites like the New York Times.
Table of Contents (13 chapters)
6
Finding and Working with Geographic Data

Finding the Canvas object under the mouse - Picking

We’ve done zooming and rotating. Let’s celebrate by adding another key piece of interactivity: the mouseover. In fact, we don’t want just any mouseover. We want to mouse over an object drawn on the Canvas and retrieve information from that object. Once we have that, we have a lot—we can create tooltips, we can highlight the object, we can link views with another graph showing the same data point, and so on.

Picking, the theory

So, how are we doing this? As established many times above, we can’t just add a listener to a set of pixels, because an event is an object maintained by the browser, interacting with DOM nodes. However, our browser...