Extended response to MadLetter's good point about the river names: I think there are three separate issues here: rivers in which the word "River" is never (or almost never) part of the name (like the Euphrates or the Danube), rivers where the word "River" is part of the name but is often dropped (like the Amazon River or the River Thames), and cultures that have different naming conventions.
The first category is not presently represented on my map, which may or may not be realistic... The Torlak River was recently renamed in order to promote nationalistic tendencies among the subjects of the Torlak Empire. It's previous name was "The Agraz" I think, although that's not official canon yet. Also, the Dornal River was called "Dorn" or "Dornflow" back in the days when a civilization flourished on its shores.
The second category is pretty common in Tornalia...the Evinelle, Hest, Tronghai, and Evarka are examples. I made a conscious decision to label all rivers and other geographical features with their full names, unabbreviated.
Third, cultural differences: the Arven language requires that river names include the element that translates to "River." I think a number of real languages do the same. As a result, the human cultures always use the word "River" when referring to rivers that flow through Arveia. And some river names are exonyms...Burnt River is called a completely different name by the goblins who live nearby, the Tsaangkil River is called "Tsaangkil" by those who live on its shores (and "-kil" means river in their language,* so "Tsaangkil River" is technically redundant), and those who live by the Ngabu River simply call it "Ngabu" (meaning "Mother Water" or something like that). The labels on the map reflect the usage of the dominant cultures (Torlaki, Loranian, and to an extent the Arven and Valnor) rather than local usage.
Of course, the shorter and more direct answer is that I'm from North America, where pretty much all of the major rivers have "River" (or "Rio") in the name, so that's what I'm familiar with and I'm sure that subconsciously influenced me.
*no, they don't speak Dutch...