When I lived in NYC I walked so much and I was in suprizingly good shape from it,even though I weighed 180 when I lived there 2 yrs. ago! I always poo pood walking, as real exercise, but I weighed 180 then and now I weight 205 two years later. no walking. so there you go!
My legs looked a lot better... even fat. You can always take a cab if the weather is really bad, and it is really good not to have a car in a city ( parking hassles + cost of garage parking) .
If you want to get a car for some reason, rent a Zip car... you can rent them for an hour, a week, a day, a month...etc.
This is proven:
WITH EXERCISE, IT IS WHAT YOU DO CONSISTENTLY THAT YOU REALLY SEE RESULTS FROM.