A city that is walkable is also served by transit. Cities like New York, Philadelphia, and DC, are walkable with extensive and convenient transit. Cities like Portland, Denver, and Los Angeles were built around transit, first the streetcar and now light rail. They are somewhat less dense and a little less walkable than the first group. As transit cities densify they become more walkable. Their goal is to become truly "walkable cities," and they are making a great deal of progress.
Driving cities, like Phoenix, Dallas, or Charlotte, have a disproportionate share of land that is accessible only by the automobile. Those cities are striving, also, to densify and create walkable neighborhoods and connect them to transit. Slowly, these cities have aspirations to become the "transit city" and even, in part, the "walkable city."