Generally, an informative visualization of any data should:
- Make as much of the data discoverable (e.g. by providing some form of indexing)
- Have clear relationships between the values associated with variables and the relative amount of ink used in rendering symbols of those variables.
Of course, there are many more similar statements that we might make, but these, in my mind are two of the most important.
Tags - which I generally distrust - are often represented by tag clouds. Tag clouds, in a certain popular form, index their content by alphabetising the tags - you can scan through the tags to find a certain tag. They indicate the frequency (or other variable) of the tag by the size (generally the font size) used to render the tag.
Considering this last point - it means that the amount of ink that a tag receives is a function not only of the frequency of the tag, but also of the length of the string. In general, if the tags are all of a similar length, then this is not an issue. However, when people start using tags with length greater than, say, 10 characters, they can gain visibility not consistent with their frequency of use.
As I said, I don't like tags too much - or rather, they are being hyped for qualities inconsitent with their usage. However, I would offer the following tag guidlines:
- Don't be tempted to use morphological varients. E.g. Sifry's use of 'tag', 'tags', 'tagging' is noisy (and only goes to further the argument that folsonomies are broken).
- If you find yourself placing conjunctions in your tag (e.g. 'blogging and search') then you probably want to use two tags. Multiple tags may indicate a conjunction of topics.
- Don't decorate your tags with syntactic elements: 'Always-on Panopticon...or Cooperation Amplifier' (Howard Rheingold - fellow Corante Network blogger).
- If your tags are made public, chose tags that are informative to not just your regular readers, but to a reasonably informed new reader (see #3).
- Be consistent. Don't use 'blogs' in one post and 'weblogs' in another. If you find yourself using a disjunction in your tag, it probably means you don't have a clear description of your topic, or that you are spamming tagging systems by using synonyms.
Tagging is a very broken idea (I mean, capitalization!). I've always believed that they are worth keeping around because someone will build neat tools on them (e.g. flickr's tag clustering is pretty cool). Tag clouds are interesting, but can amplify the types of problems I have outlined above. Have a look at the tag cloud on Corante's Web Hub, and compare it with that created by Joi Ito. But then, it is no surprise that Joi gets tagging...