From the Scottish Government Website:
Physical distancing, hand hygiene and respiratory hygiene are the most important and effective things we can all do to prevent the spread of coronavirus. The wearing of face coverings must not be used as an alternative to any of these other precautions.
There is evidence that face coverings have some additional value, especially in crowded and less well ventilated spaces, and where 2m distancing is not possible.
In indoor places and where physical distancing is difficult and where there is a risk of contact within 2m with people who are not members of your household, you are expected to wear a face covering.
People must by law wear a face covering in shops, on public transport and public transport premises such as railway and bus stations and airports, and in certain other indoor public places.
There is no evidence to suggest there might be a benefit outdoors from wearing a face covering unless in a crowded situation.
To read the full guidance - visit The Scot Gov website by following this link https://www.gov.scot/publications/coronavirus-covid-19-phase-3-staying-safe-and-protecting-others/pages/face-coverings/