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> This is actually a map representing watersheds in the continental United States, not rivers. Rivers can be either actual or perennial. This however is just showing the drainage patterns of the watersheds, which include rivers, creeks and streams, but it is wrong to assume that these are all real rivers.
Well, sort of. The map is not showing watersheds/drainage basins. It is showing rivers, streams, creeks, brooks, arroyos, washes, and so on, and calling the whole lot “rivers” in the generic sense.
Somewhere in these comments is a link to the source, which is the [National Hydrology Dataset](http://nhd.usgs.gov/)—the “stream” part, not the “lake” or “watershed boundary” parts.
The USGS points out ([here](http://geonames.usgs.gov/domestic/faqs.htm)) that “there are no official definitions for generic terms as applied to geographic features”, so they use a set of generic terms for feature types, like lake, summit, and stream. They use “stream” for all “linear flowing bodies of water”, as they put it. That is what this map shows, except the title of this post uses the word river instead of stream. Either way it is meant as a generic general term.
The thing is, English does not have a simple generic term to use here. Nor are there universal, general definitions of words like river or stream. Sometimes “river” is used in a well-defined way, sometimes not. In this case, “river” is being used in the general, generic sense.