Considering several basins together as a whole can be helpful when they are nested within a larger common basin. For example, Sears, Valley, Goff, West Tributary, Richards, and Sunset Creeks all flow into Kelsey Creek. If a salmon goes up the mouth of Kelsey Creek, it could eventually end up in any one of those basins! Likewise, stream flow or pollution concerns in lower Kelsey Creek may originate in any one of those basins upstream.
Multiple small streams that all flow into a common water body may be clustered together under one basin area name for convenience. The small streams in the North Lake Sammamish and very close together and similar in land use. When comparing them to other basins, it can be more useful to consider them as a whole.