command area is a part of catchment area.But catchment area is the area between the boundary line that is connected by highest elevation points on a specific area under observation.This may or may not be the command area.But command area is which area comes under culturable area.When irrigation is applied to any particular land,the area that need to be or u wanted to be irrigated is called as the command area.
There are different areas as well like Gross command area(G.C.A) and culturable command area(C.C.A).