IS: 4986-1968 Guidelines
The Bureau of Indian Standard (BIS) suggests that one raingauge up to 500 sq. km might be sufficient
in non-orographic regions. In regions of moderate elevation (up to 1000 m above msl), the network
density might be one raingauge for 260 - 390 sq. km. In predominantly hilly areas and areas of heavy
rainfall, the density recommended is one for 130 sq. km.