Situated on 40 hills of varying heights—among the highest are Telegraph Hill, Nob Hill, and Russian Hill—San Francisco is known for its steep streets, many of which ascend and descend hillsides, the result of insistence by early planners on imposing a strict grid pattern on the city rather than following the natural contours of the land. The two hills of Twin Peaks mark the geographic center of the city, which is divided into a number of distinct