According to the United States Census Bureau, the city has an area of 34.7 square miles (90km2), of which 19.4 square miles (50km2) is land and 15.2 square miles (39km2) (43.91%) is water. A major watercourse draining much of Redwood City is Redwood Creek, to which several significant river deltas connect, the largest of which is Westpoint Slough.
Redwood City's sphere of influence includes the districts of Emerald Lake Hills and North Fair Oaks, which, however, are largely outside the city boundaries and are counted individually for the U.S. census. Palomar Park, just north of Emerald Hills and east of San Carlos' Crestview area, is another Redwood City neighborhood that is formally part of unincorporated San Mateo County. The northern neighborhood of Redwood Shoresis part of Redwood City, although it is not possible to travel by road from one to the other without passing through the neighboring city of San Carlos, or through Belmont via unincorporated San Mateo County. Although Redwood City has a large middle-class, the south eastern section of Redwood City highly resembles working-class North Fair Oaks in demographic make-up and income level.