Researchers at Georgia Tech have put together a nice web app that computes the probability of encountering a SARS-CoV-2 positive person in a randomly sampled group of size N in each county in the USA, with N varying from 10 up to 10,000.
Here is an article that describes their underlying assumptions.
I think this is very useful for two purposes:
To find the relative risk of encountering someone who is CoV+ in different counties around the country.
To realize how prevalent the virus is in many locations, especially those recently experiencing surges, and that even for small to moderate size groups, the probability of encountering someone is higher than one thinks.
The take home message is the same take home message I try to emphasize these days: don't take this virus lightly, and be diligent to practice the basic precautions of avoiding spending long periods of time in crowded, indoor settings, especially if poorly ventilated, and practice basic social distancing and wear masks when around other people indoors!