Announcing Unicode 7.0

For example, some are phonographic (the letters represent phonemes, i.e. speech sounds), others are logographic (the letters represent words, or morphemes).

Both of these can be featural: The Korean Hangul script is phonographic, but the letter shapes are not arbitrary. Some of them are visualizations of mouth shape or tongue position when producing the sound. For example the velar consonant ㄱ (somewhere inbetween the English g and k, roughly) is the tongue position as seen from the side.

A logogram can also be featural, i.e. it can look like the thing it represents. This would be the case for a glyph that means "thermometer" and looks to viewers like a thermometer. It could also be arbitrary - some shape that you just agree on to mean thermometer. Perhaps sharing some graphical aspects with topically related logograms.

They're all just spots on a spectrum.

(Edit: I briefly touched on pictograms vs. ideograms a bit more down below.)

If you look at FontAwesome, it uses characters in the "unicode private use area" -- which are effectively undefined -- but putting those codepoints in your HTML document while having the appropriate font loaded will show the appropriate icon glyphs.

A fair bunch of Chinese characters are also actually pictographic (they're an image of something) or ideographic (they represent an abstract idea, not a morpheme or word) in origin, if not current usage.

This stuff - synergies and conflicts between writing systems and various media - fascinates me. Chinese writing for example now suffers from the problem that if your medium doesn't allow free-form painting/graphical compositing (like our computers largely don't right now) you can't easily coin new logograms, since you need a central registry that's slow to distribute to leaf nodes (cf. Unicode). So what's happening now is that new words get coined by recombining existing characters based on their sound value, adding a phonographic layer on top. And of course inputting Chinese has also become dependent on auxiliary systems like pinyin-based IMEs.

Meanwhile, the Korean Hangul alphabet has the interesting property that some of the letters graphically derive from each other with consistent patterns of "take this, add a stroke and you get this", making it easier to design keyboards with reduced numbers of buttons to enter combos. There's the theory that this contributed to the success of texting/mobile in Korea, and is a contributing reason for the healthy mobile industry there.

I'm getting far from the original topic with this rambling, but it still reads on it in one sense: There's a lot of variety to writing systems, and it's worth thinking about emoji as a spot on the spectrum instead of in isolation.