What is the scope of a federal agency's "action area" and what is the test for determining its scope?

"Action area" is defined as "all areas to be affected directly or indirectly by the Federal action and not merely the immediate area involved in the action." 50 C.F.R. 402.02. Generally, "determination of the scope of an analysis area requires application of scientific methodology and, as such, is within the agency's discretion." Native Ecosystems Council v. Dombeck, 304 F.3d 886, 902 (9th Cir. 2002). To withstand judicial scrutiny, the agency must explain the "scientific methodology, relevant facts, or rational connections linking the project's potential impacts" to the action area boundaries. Id.