Is it normal to be able to see / feel a cats spine?

[HoneyDragon]

I've seen a lovely chatty cat twice now, but he seems very thin. Lovely fur, doesn't appear to be a stray.

But I don't know what's normal thin and what's too thin and whether I should cat nap it and take it to the vet.

The cat is in mid-walk in the photo though...so it's not really a clear indication of it's state of health.

No, nothing is one hundred per cent sure, but to me it has the look of an ill cat. As I said I see a lot of ill/starving cats and you just get to recognise the look. I'm not saying I can't be wrong but it's certainly worth checking out.