Please answer a question about the following article about Boston:

Nicknamed "The Walking City", Boston hosts more pedestrian commuters than do other comparably populated cities. Owing to factors such as the compactness of the city and large student population, 13 percent of the population commutes by foot, making it the highest percentage of pedestrian commuters in the country out of the major American cities. In 2011, Walk Score ranked Boston the third most walkable city in the United States. As of 2015[update], Walk Score still ranks Boston as the third most walkable US city, with a Walk Score of 80, a Transit Score of 75, and a Bike Score of 70.

What is Bostons nickname?
The Walking City