I bought this book years ago when learning trees, and it is hands-down one of the best books for doing so. Intuitive organization, accurate descriptions, and notes where in the city the trees are most common. This guide was clearly a labor of love for the authors, and the product is remarkable.
It is particularly invaluable because it includes ALL the trees you can find in the city, even ones that are only found on streets or planted as decor. Unfortunately many (inferior) tree guides only include "natural" trees in forests and are therefore useless in a city.
This book is an absolute gem and a necessary companion for your daily Washington constitutionals. They have packed in incredible detail and insights into the Washington landscape in this single volume. Must buy. The sublime organization of the index alone is worth five stars.