old variant of 坰[jiong1]
A plot of land 口 surrounded by a border 冂; 冂 also provides the pronunciation
《說文》：“冂，邑外謂之郊，郊外謂之野，野外謂之林，林外謂之冂，象遠界也。冋，古文冂。从囗，象國邑。坰，冋或从土。”