“附廓区”可以译为 "suburban districts adjacent to the city proper" 或更简洁地表达为 "adjacent suburban areas"（若上下文明确是围绕某城市时）。
附廓：字面意为“紧邻城墙的郊区”，英文中常用 "suburban"（郊区的）或 "adjacent"（相邻的）搭配 "districts/areas" 来表达。
城市主体：若需强调与城市主体的关系，可补充 "to the city proper"（“proper”指城市核心区）。
The adjacent suburban areas (附廓区) have witnessed rapid development in recent years.
The planning of suburban districts adjacent to the city proper (附廓区) requires integrated urban-rural strategies.
根据具体语境选择更贴切的表述即可。