Sorry. Stupid question. Deleted.

I guess you may as well ask where you reside - as that is the place most people will do there shooting, no?

Buggers, you're right! Sorry about that. It does say US content as well, so people in Timbuktu could shoot US subjects or images and never leave home. But none-the-less, you are correct, there should be a zero option. Done.

You missed out the zero option ! Most people in the world have never visited the USA.

In your best estimate what percentage of your images on SS are US source material, or shot in the USA?

The reason for the questions are to determine if localized photos sell better in the country of origin, and the USA is the only one that separate reporting on SS.

0%
Last time I went in USA was in 1979�

I carry a Swiss Army Knife, have since about the time of your experience. Some of the security regulations are stupid and accomplish nothing, but to aggravate people. At the courthouse they were taking away nail clippers with files on them. Federal courthouse building, you can't have a pen knife. (trip back to the car to leave my knife, should I forget, at all of these places)

What next pencils and ball point pens? 

It's all about appearance, nothing to do with reality. And yes I'd agree with you, it's all an overreaction. Like no photos in train stations? Yeah very sneaky, a guy with a DSLR walking around with a big white lens. That's a threat.

No dummies... almost everyone has a camera in their pocket, built into their phone!

I was there in 1977, and I was held up by the marines at the gate of the White House because I carried a knife.
I thought they over reacted a bit.

Had it been nowadays, I would still have been there. Dead or  alive.

Interesting question. I went through and counted up my US images - US travel, US editorial, and nature images that are site specific. That came to 34% of my portfolio but they account for 65% of my all time sales at shutterstock.
I did not count isolated objects and other still life photos that could have been shot anywhere unless they were of iconic American things, nor did I count abstract backgrounds, since, though many of these were shot in the US, again they could be anywhere.
Since this is the time of year for analyzing sales and deciding what to shoot in 2014, I also went through my payment history and discovered that 51% of my sales come from US sources and 49% from non-US sources, so clearly customers outside the US are purchasing US source images - I've found a lot of my US images - travel and editorial - on South American and European web sites and I often have sales from every single continent showing up on my map at SS. Though my image with the highest number of sales is an abstract background, my highest grossing image there is a US travel image.
Most of my European images (I've only been to North America and Europe) are with traditional agencies or are only available through my own site, but I checked out those stats too. They make up just 3% of my portfolio and account for 0.6% of my sales - with such tiny numbers I don't think the stats are significant, though the percentages are about the same for European images on DT, a European site.
I've sold a lot of US travel photos on Alamy too - many to European clients - in the UK, Italy and Russia.