国立美術館 : マップと概略案内. (OCLC #906972890)
RDA 3.5.1.4.11 on Dimensions of Sheets says, for folded sheets not intended to be read in pages, “record the height × width when extended followed by the height × width when folded” as in:
46 x 46 cm folded to 12 x 23 cm
Commission on Security and Cooperation in Europe. (OCLC #43026739)
This government document is a single sheet of paper, folded like a tri-fold brochure (and housed in an envelope to protect it).
RDA 3.4.5.14 on extent of Single Sheets says “if the sheet is designed to be read in pages when folded, record the extent as 1 folded sheet followed by the number of pages laid out on the sheet, in parentheses.”
RDA 3.5.1.4.11 on dimensions of Single Sheets says “if the sheet is designed to be read in pages when folded, record only the height of the sheet when folded” (as though it is a volume).
So for this document, the physical description is:
300 __ ǂa 1 folded sheet (6 pages) ; ǂc 22 cm