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Thanks, credit card suggests perfectly flat. Second hand bike so hard to say on useage, definitely quite old rims but seems not used that much. Will buy some new brake pads/clean them and see if this gives a cleaner braking feel.
___freddie
Sergeant_Pluck
Impossible to tell from that particular photo. If you hold something flat (edge of credit card is popular) against the braking surface you'll be able to see how concave or not the surface is. If you can see a large crescent of daylight between the straight edge and the braking surface then they're on the way out, but precisely when they are worn to dangerous levels is hard to say.
Some rims have a braking wear mark on them which disappears when the surface is significantly worn down, but it varies between manufacturers and rims. If they feel super concave, you've had them for yonks, you're a heavy rider, you ride in hilly areas, you ride in the rain, you ride in gritty conditions, or any of the above, and you're not quite sure - perhaps bin them. I've seen rims explode while riding and even burst when left out in the sun (tyre and tube expand in the heat and pop through the wafer-thin braking surface).
Those are extremes though and you may have 1000s of kms left in them!