Create Beautiful Visualizations that Free Your Data to Tell Powerful Truths “The depth of Barrett Clark’s knowledge shines through in his writing: clear, concise, and confident. Barrett has been practicing all of this stuff in his day job for many years–Postgres, D3, GIS, all of it. The knowledge in this book is real-world and hard-earned!” –From the Foreword by Obie Fernandez Data Visualization Toolkit is your hands-on, practical, and holistic guide to the art of visualizing data. You’ll learn how to use Rails, jQuery, D3, Leaflet, PostgreSQL, and PostGIS together, creating beautiful visualizations and maps that give your data a voice and to make it “dance.”   Barrett Clark teaches through real-world problems and examples developed specifically to illuminate every technique you need to generate stunningly effective visualizations. You’ll move from the absolute basics toward deep dives, mastering diverse visualizations and discovering when to use each. Along the way, you’ll build three start-to-finish visualization applications, using actual real estate, weather, and travel datasets.   Clark addresses every component of data visualization: your data, database, application server, visualization libraries, and more. He explains data transformations; presents expert techniques in JavaScript, Ruby, and SQL; and illuminates key concepts associated with both descriptive statistics and geospatial data. Throughout, everything is aimed at one goal: to help you cut through the clutter and let your data tell all it can.   This guide will help you Explore and understand the data visualization technology stack Master the thought process and steps involved in importing data Extract, transform, and load data in usable, reliable form Handle spotty data, or data that doesn’t line up with what your chart expects Use D3 to build pie and bar charts, scatter and box plots, and more Work effectively with time-series data Tweak Ruby and SQL to optimize performance with large datasets Use raw SQL in Rails: window functions, subqueries, and common table expressions Build chord diagrams and time-series aggregates Use separate databases or schema for reporting databases Integrate geographical data via geospatial SQL queries Construct maps with Leaflet and Rails Query geospatial data the “Rails way” and the “raw SQL way”

Table of Contents:
Foreword xv Preface xvii Acknowledgments xxiii About the Author xxv   Part I: ActiveRecord and D3 1 Chapter 1: D3 and Rails 3 Your Toolbox—A Three-Ring Circus 3 Maryland Residential Sales App 5 Summary 17   Chapter 2: Transforming Data with ActiveRecord and D3 19 Pie Chart Revisited 19 Bar Chart 24 Scatter Plot 28 Scatter Plot Revisited 33 Box Plot 34 Summary 40   Chapter 3: Working with Time Series Data 41 Historic Daily Weather Data 41 Weather Rails App 42 Simple Line Graph 45 Tweak 1: Simple Multiline Graph 50 Tweak 2: Add Circle to Highlight the Maximum Temperature 51 Tweak 3: Add Circle to Highlight the Minimum Temperature 53 Tweak 4: Add Text to Display the Temperature Change 55 Tweak 5: Add a Line Between the Focus Circles 56 Summary 58   Chapter 4: Working with Large Datasets 59 Git and Large Files 59 The Cloud 60 Hotlinking 60 Benchmarking 62 Querying “Big Data” 65 When Benchmarks and Statistics Lie 68 Summary 69   Part II: Using SQL in Rails 71 Chapter 5: Window Functions, Subqueries, and Common Table Expression 73 Why Use SQL? 73 User-Defined Functions 75 How to Use SQL in Rails 78 Scatter Plot with Mortgage Payment 79 Window Functions 81 Using Subqueries 84 Common Table Expression 84 CTE and the Heatmap 86 Summary 90   Chapter 6: The Chord Diagram 93 The Matrix Is the Truth 93 Flight Departures Data 94 Departures App 95 Transforming the Data 101 Create the Views 104 Draw the Chord Diagram 106 Disjointed City Pairs 108 Summary 113   Chapter 7: Time Series Aggregates in Postgres 115 Finding Flight Segments 115 Graphing the Timeline 121 Summary 127   Chapter 8: Using a Separate Reporting Database 129 Transactional versus Reporting Databases 129 Working with Multiple Schemas in Rails 131 Creating Objects in the Reporting Schema 132 Summary 138   Part III: Geospatial Rails 139 Chapter 9: Working with Geospatial Data in Rails 141 GIS Primer 141 PostGIS 144 ActiveRecord and PostGIS 146 Using Geospatial Data in Rails 147 Working with Shapefiles 150 Summary 154   Chapter 10: Making Maps with Leaflet and Rails 155 Leaflet 155 Incorporating Leaflet into Rails to Visualize Weather Stations 157 Visualizing Airports 163 Visualizing Zip Codes 168 Summary 181   Chapter 11: Querying Geospatial Data 183 Finding Items within a Bounding Box 183 Writing a Bounding Box Query 184 Finding Items Near a Point 187 Calculating Distance 190 Summary 191   Afterword 193   Appendix A: Ruby and Rails Setup 195 Install Ruby 195 Finalize the Setup 199   Appendix B: Brief Postgres Overview 201 Installing Postgres 201 SQL Tools 202 Bulk Importing Data 202 The Query Plan 204   Appendix C: SQL Join Overview 207 Join Example Database Setup 207 Inner Join 207 Left Outer Join 208 Right Outer Join 208 Full Outer Join 209 Cross Join 209 Self Join 209   Index 211