A shelter with one wall open — a roof leaning against a rock face rather than a closed house. As a radical it frames buildings that are wide and public: 店 (shop), 库 (storehouse), 座 (seat), 庭 (courtyard). From the open shelter came the sense of breadth itself.
广 names Guangdong and Guangzhou, and the language 广东话 (Cantonese). 广告 is advertising ('broadly announce'), 广场 a public square, 广播 a broadcast. The traditional form 廣 packed 黄 inside the shelter; simplification emptied the room out completely.
A roof leaning out from a cliff, one side wide open — BROAD, not enclosed.
广 is one of the most aggressive simplifications in the language: the traditional 廣 had 黄 under the roof, and the reform simply deleted everything inside.