Heather Schwartz 
Codes and Zones [PDF ebook] 

Why do we use time zones, area codes, and zip codes? This social studies book explains how these codes and zones work and why they came to be. Do you know how many time zones used around the world today? Or how many area codes people use in the United States? Students will find the answers to these questions and more in this exciting teacher-approved book. With a glossary and index, essential discussion questions, and other helpful features, this book explores time zones, area codes, and zip codes in a fun and meaningful way.