"It also applies to sidewalks, streets, paths, and squares. And there are no exceptions for joggers and cyclists."
"Somerville’s order — which takes effect on Wednesday, but with a one-week grace period — comes with a potential $300 fine. And unlike in Brookline, city officials say it will be enforced by Somerville police."
https://www.boston.com/news/coronavirus/2020/04/27/somerville-face-covering-mask-order-coronavirus