RE: New York vs. California ....
More densely packed population? Less public transit and transit being cleaned more often?
Those are two of the most significant in my mind. First of all when you are in NY, just to get to the sidewalk you are likely touching knobs, stairways rails, elevator buttons and the like. Not to mention people crammed in elevators breathing on each other. Then go through the process to get on a subway. Stairway rails, ticket machines, putting you plastic ticket through a machine that has had thousands of others in it that day and then get it back and put it in your wallet. Railings, then the door opens on the subway and you grab a handle to get in sit down or stand up with people breathing on you. Have to switch trains?, then repeat the process within the subway station. When you finally arrive at your destination, repeat the entrance process in reverse.
In Cali, you walk out to your car and drive to where you are going. That's pretty much it for most people.
Even in food stores, if you have ever been in the City, you know that they are typically VERY "condensed" if that is the right word. There is a chain of markets in the City called Key Food. They are spread all over the city. They are neighborhood food markets which many of us would consider the size of a postage stamp. Perhaps the size or two 7-11's put together or something like that. Yet they have a deli, hot foods, a salad bar and most things that larger stores have, but just in a very small footprint. And guess what, the aisles are so narrow that it is difficult at times for two people to easily pass each other. So again, more close contact.
In Cali, you drive to the big food stores (like Von's, Safeway, etc.) and the aisles are wide and you can much easier avoid getting close to anyone. When you are done, get back in your car and drive home.
So I think think there is no comparison between New York and California. One is just spread out, the other is just so condensed.
Rub a Dub