Perhaps walking is best imagined as an 'indicator species,' to use an ecologist's term. An indicator species signifies the health of an ecosystem, and its endangerment or diminishment can be an early warning sign of systemic trouble. Walking is an indicator species for various kinds of freedom and pleasures: free time, free and alluring space, and unhindered bodies.

Wanderlust: A History of Walking (ed. Penguin, 2001) - ISBN: 9781101199558