We tend to think that art is centered in metropolitan ideas. Here comes an exhibit to show us it ain't necessarily so. At the Clayworks, "Edges and Boundaries" brings together ceramics by artists working in rural areas of Maryland. It includes sculpture, functional pottery and wall pieces by artists living as far afield as Frostburg, Salisbury, La Plata, Accokeek, Princess Anne, Thurmont and Gapland. The show was organized by Deborah Bedwell, Baltimore Clayworks' executive director, and after it closes in Baltimore, it will make an extensive tour of as many as eight other sites in Maryland, including Frostburg State University and University of Maryland Eastern Shore at Princess Anne.