What determines the sorting order of images on a page

[Big Frank]

I'm doing a website with a gallery of images. No widgets, just images placed on a grid and a pop-up displays a zoomed when clicked on.
The zoomed image controls allow you to click "next" and "previous" but they don't display in the order as shown on the page.
If ImageG is next to ImageA, how to I ensure that is the same order when clicking the next and previous buttons?
After all this time I thought I knew this stuff.
I was wrong.
Any help gratefully received.

PS. I have three variants of the website and the order isn't necessarily the same in each variant.

[Acorn]

I'm doing a website with a gallery of images. No widgets, just images placed on a grid and a pop-up displays a zoomed when clicked on.
The zoomed image controls allow you to click "next" and "previous" but they don't display in the order as shown on the page.
If ImageG is next to ImageA, how to I ensure that is the same order when clicking the next and previous buttons?
After all this time I thought I knew this stuff.
I was wrong.
Any help gratefully received.

PS. I have three variants of the website and the order isn't necessarily the same in each variant.

BF, you need to ensure the order in the Page and Layout gallery for each Variant for your image collection. Put all the images together so they are consecutive in the tree structure and then put Image A over image B over Image...

Acorn

[Big Frank]

[post deleted]
Never mind, I'm an idiot.

Many thanks for the extremely helpful tip Acorn!