"Gangshan region" (岡山地區) is unofficial but used in some contexts. The boundary of this region is based on the Okayama-gun (岡山郡) in the Japanese era.
Projection: TWD97 (≈ WGS84)
Geographic limits of the map:
West: 120° 9' 39.6'' E (120.161 E)
East: 120° 27' 54'' E (120.465 E)
North: 22° 55' 40.8'' N (22.928 N)
South: 22° 42' 46.8'' N (22.713 N)
Own work
A-lú-mih