Here is a useful graphic from the US Centers for Disease Control and Prevention. The graphic described situations for when masks are required. I don’t want to use preferred because it means people may opt out of using masks. It is a useful reference even for those in other countries that do not have enough clear information from their governments about wearing masks and how it helps protect vs. getting infected by Covid-19. It is applicable to people searching for a legit reference to mask-wearing in outdoor situations.
This information becomes more relevant as people start getting vaccinated and at the same time look forward to getting together with family and friends in social events such as eating out or having picnics. Of course, this also applies to exercise as well as commuting via active transport modes (i.e., walking or cycling).