Is that a plane or a city? It is difficult to say which of the world's largest and best known metropolises I love more.

These passions are still as important to me as they were when I was a child in my hometown. When I was a kid, I couldn't decide between finishing the assembly of my latest model airplane and reading the names of the cities on it.

My new book, Imagine a City: A Pilot's Journey Across the Urban World, is both a memoir and a pilot's love letter to our planet's great metropolises. As travelers return this summer, I hope a pilot's perspective will help them remember how amazing cities are and how fascinating they are to visit.

Frequent fliers use three-letter codes when speaking of cities. I would text a pilot friend: I am back from YYZ on Monday at 10am, how about coffee at LHR? When entering our destination in the aircraft's navigation computers, we use a separate set of four-letter codes, which are known as CYYZ, EGLL, and ZBAD.

In a world without cities and their need for connection, airliners wouldn't make sense, and pilots today experience the urban world in a way that no one else has before. I have flown from London to cities such as Beijing, Istanbul and Lisbon more than a dozen times.

In the days leading up to a flight, I might find myself looking forward to a hike and the view from a particular hill, followed by a few hours at the nearby cafe that serves the best breakfast burritos. The hill I am thinking of is in Lisbon. What about those burritos? The people are in Phoenix.

An older colleague used to carry a diary with him wherever he flew, so that after he retired, he could easily remember where he'd been. Along with my legally mandated fields such as the aircraft registration and the departure and arrival times of each flight, I record hasty notes on some of the world's great cities. The bookstore café south of the hotel was closed. A day trip to Kamakura is recommended. The old olympic pool is cool.

I am struck by how easy it is to talk about cities in basic human terms, such as lungs, arteries, hearts, characters and even siblings. I like the idea that each city is formed from smaller entities that may only rarely, if ever, consider the part they play in its entirety.

It is obvious to pilots that cities are sculpted by nature before they are built by people. An aerial route can run close to a river. In Europe, this occurs most often on flights between London and Bucharest, when we might first spot the Danube as we pass north ofMunich, before following its path through the hearts of Vienna, Bratislava, and Budapest, where we say farewell.

On flights from London to Jeddah, we follow the Nile from its Mediterranean delta south through Cairo and Luxor, and on overnight flights the life-giving river appears to be made of light. The home of some of our planet, as we look down on it, may be seen by both the Tigris and the Euphrates, a reminder that "Mesopotamia" means "the land between the river" in Ancient Greek.

A friend will ask me what my favorite city is. It depends on the season, climate and beauty of Cape Town, for example, and on where I might cross, for example, San Francisco. In high school, I lived in Japan for a summer and fell in love with the place. Whenever I fly to Tokyo, I am amazed at the size of the city.

It is difficult to say which is the most striking from the air. It's always special to me when a nocturnal approach over London takes place.

Los Angeles may be the most amazing place to land after dark. The most impressive time to fly in to Los Angeles is at night, when all the lights are on and the city is below you. I know what she means when I descend over the dense and shiny circuitry that lies between the curtain of mountains and the matt and dark waters of the open Pacific.

There is a city in western Massachusetts. On flights between London and Dallas and New Orleans, I see my hometown most often. No one would mistake the nightscape for that of Boston or New York. I know which set of lights to look for in western New England after 20 years of flying.

In middle age, when I see the glow where my first journeys began, I feel like I have a copy of my own memories.

When no cockpit view lasts long when you're traveling 85% of the speed of sound, I think of my parents. They have been gone for a long time, but it is easy to remember the days when a steaming casserole is taken out of the oven and laid to cool on the stove.

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