Keycap Profiles

Cherry

Keyboards of Cherry brand (Cherry is a German company).

OEM

Original Equipment Manufacturer. It means, a typical cheap keyboard.

SA

“spherical angled” or “spherical all-rows”, from Signature Plastics (a USA company that makes keycaps).

XDA

Not sure what it means.

DSA

Not sure what it means. Probably a name originated from Signature Plastics.

Basically, key profile are of 2 types:

• Uniform → all keycaps are shaped the same.
• Non-uniform → Each row has a different shaped keycap.

There are 3 shapes of keycap's top:

• Flat
• Concave (aka spherical)
• Convex. (usually for the spacebar key.)

Another issue, is how the key plate is shaped:

• Flat. (like laptop.)
• Staircase. (like a mechanical typewriter. [see Smith Premier Typewriter] )
• Curved (Example: Kinesis Advantage2, Microsoft Sculpt Ergonomic Keyboard )

Conclusion

I think the best key profile is uniform with concave top. Concave top helps your finger determine position of the key. Uniform is great for swapping keycaps.

Those non-uniform keycap profiles are a hack, to make up for flat key-plate. We should use a curved plate if one really want a ergonomic fit.