How do I tell the difference between two split keyboards?

At splitkb.com, we like to make our keyboards in series which all share the same feature set, for example the Halcyon Series with preassembled keyboards, and the Aurora Series of DIY keyboards.

With all those features the same, what then is the difference between two split keyboards? The answer lies in its layout.

A split keyboard consists of a few common layout blocks:

• The alpha block consists of the keys that output letters. On a common keyboard, this block starts with QWERTY. On most keyboards, this block consists of 30 keys, which are a block of 3x5 keys per half of a split keyboard.
• The number row is a row of keys above the alpha block, and is equivalent to the number row on a common keyboard. It usually outputs the numbers, and their corresponding symbols when the Shift key is held. On a keyboard without a number row, the numbers are moved to a layer instead.
• The thumb cluster are the keys placed below the alpha block, and are accessed with the thumb.
• The outer column is a column of keys placed next to the alpha block, on the "outside", facing furthest away from the other half of the keyboard. Usually, keys such as Escape and Tab are placed here, as well as the quote key ' ".
• It's quite rare, but some keyboards also have an inner column, placed next to the alpha block on the side nearest to the other half of the keyboard. As with any key, these can be used for whatever you'd like them to, such as macros.

With these blocks of keys, a layout can then be described by a few common properties:

• Stagger is the way in which the alpha block of keys is laid out relative to one another. It's divided in two aspects:
  • Stagger type is the main way they're laid out. A normal, common keyboard has row stagger, in which the keys are laid out on straight rows. Split keyboards usually offer columnar stagger, in which the keys are laid out in columns, instead of in rows. Lastly, when the keys are laid out in a grid (equally in rows as in columns), it can be called ortholinear.
  • Stagger aggressiveness determines the offset between the different rows or columns of keys. A mild stagger means there's only little difference in offset, while an aggressive stagger means the difference is large.
• Spacing determines the space between the center points of each switch. Most common is MX spacing, which places switches at a default distance of 19.05mm by 19.05mm. Other spacings also exist, such as choc spacing, which is usually 18mm by 17mm, though this can vary. The kits sold at splitkb.com commonly use MX spacing.
• The thumb cluster position determines where the thumb keys are placed relative to the main block of keys. Some keyboards place these closer to the alpha block, while others move them further out.

Lastly, the key count and the presence of the various blocks determine the layout.