Not All Rivers Reach the Sea - NYTimes.com about half way through the article I read “within a 250-mile radius of its banks. “ This seems to me to be a curious or unfamiliar use of “radius”. I always thought “radius” was from a central point. Have I been wrong all these years?

curious or unfamiliar use

I’d go farther and call it wrong.

What the doctor said.

My dictionary has a definition for radius as “a bounded or circumscribed area.” So, I wouldn’t say that the usage is wrong.

What dictionary is that? If the area is bounded by a circle, I’d say it’s right, but that definition is woefully incomplete.

The OED definition that is nearest is:

6.a. A circular area, the extent of which is expressed as a specified distance from its centre in all directions.

As for the newspaper usage, not only is it a misuse of the word, the sentence is wordy and bloated. It more concisely and elegantly stated by just leaving it out, “within 250 miles of its banks.”

I’m not defending the quality of the prose.  I’m just making the point that if you are looking for mathematical precision you won’t often find it in the dictionary.

Radius is a word that is used precisely to mean the radius of a circle or imprecisely to mean a general area surrounding a central line or point. 

You can be a prescriptivist if you want, but where you can find in a dictionary (any dictionary) an alternative definition that contradicts your notion of a word’s meaning—that is a good indication that you should revise your view.

My dictionary at work is an old Webster’s Ninth New Collegiate Dictionary (probably 30 years old at this point).

A river represents a line, often meandering. Using radius in relation to a line, especially one of unspecified length, doesn’t pass the smell test.

Gotta say, however, that it took until this thread for me to look up the word in the dictionary and realize it is not the same root as radish and radical, which never made sense anyway.

Again, I’ll quote from one of the definitions in my old dictionary: “the distance from a center line or a point to an axis of rotation”.

But that definition is for a rotating system that is sweeping out a circle. It has nothing to do with static, linear measurement like distance from the banks of a river.

The problematic definition, however, is still current in M-W’s 11th edition. I think the editors need to take a hard look at it for the 12th. There may indeed be evidence of usage that supports it, but if so, I’ve never seen it before this, and I think it more likely that they shortened the definition too much.

Yes.  As I think about it, the use of radius with a center line is likely to address a three dimensional figure—such as the radius of a tube—where you are dealing with preccise mathenatical concepts. 

I’m not contesting that the blog post is poorly written.  However, the dictionary definition reflects that radius is used loosely to mean environs, locale or surroundings.  If you question the dictionary editors for a source for the colloquial usage, I’ll send them the blog post.  Then we can have an argument that is truly circular (so to speak).