The Digital Obstacle File (DOF) describes all known obstacles

Air traffic obstacle

An Air traffic obstacle is a tall structure which can endanger air traffic. Air traffic obstacles have to be marked in most cases with red and white colored markings and with aircraft warning lights at night. On larger structures blinking lights are required...

 of interest to aviation users in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, with limited coverage of the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, the Caribbean

Caribbean Sea

The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....

, Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 and Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. The obstacles are assigned unique numerical identifiers and accuracy codes.

These downloadable products are available at least 21 days prior to their effective date. Data updates (also known as "chart updates") are coordinated over 56-day cycles. There are six to seven of these updates per year. Editions will be listed by year and 56-day cycle number; for example, Edition 200801 was the first 56-day cycle of 2008 (i.e. February 14, 2008).