"Instacart CEO Apoorva Mehta told AllThingsD that his company built a 'feasibility matrix' to determine which city it would expand to. Components of the matrix included what you might guess: car-ownership density and income. Weather was reportedly also a factor. Mehta tells TechCrunch that '33 percent of the year, Chicago has some form of precipitation' and that his company has learned in the San Francisco area that 'people just do not like grocery shopping when it’s raining.' Seattle, you might be next."

I think Chicago is a natural fit. The specific neighborhoods they picked have about 600k people in 33 square miles (a bit denser overall than San Francisco as a whole). There are a ton of residential skyscrapers in those neighborhoods, which means they probably can hit several orders in one go. 30% of Chicago households don't have a car, about the same as San Francisco. It rains or is cold about half the year, and is hot and humid a couple of months out of the remainder, which makes people not want to carry groceries home.

Yeah, the third largest city in the US with 2.7 million people. Perhaps you've heard of it?