District 21 consist of Clementi, Upper Bukit Timah, Hume Avenue
Hume Avenue was probably named after Walter R Hume, an inventor turned entrepreneur who founded Hume Pipe Company (Australia). Today, only the old Ford Motor factory still remains as other factories made way for new private residential developments.
The KTM Malayan Railway used to operate passenger and freight services that ply through Hillview, from Malaysia in the north to Tanjong Pagar station in the south. Of significance are two railway truss bridges spanning across the undulating terrain near Hillview. Under a bilateral agreement signed between Singapore and Malaysia on 24 May 2010, the railway land has been handed back to Singapore. There are now plans to redevelop the railway land running along Hillview into a Rail Corridor. Ideas include preserving it as a green corridor, a cyclist highway with direct access into the central business district, gardens and community spaces.