http://www.audettemedia.com/blog/seo-guide-information-architecture/
What is Information Architecture? Definitions
“We shape our buildings; thereafter they shape us.” - Winston Churchill
In the classic work in the field, Information Architecture for the World Wide Web, Peter Morville defines information architecture this way:
in•for•ma•tion ar•chi•tec•ture n.
1. The structural design of shared information environments.
2. The combination of organization, labeling, search, and navigation systems within web sites and intranets.
3. The art and science of shaping information products and experiences to support usability and findability.
4. An emerging discipline and community of practice focused on bringing principles of design and architecture to the digital landscape.
With SEO, we care primarily about delivering relevant content to the spiders in a format that they can easily digest and understand, but we also care about making it usable, credible, attractive, and high-quality. SEO like IA has to be part of every aspect of web production, from the initial strategic planning phase to the on-going preservation of rankings and expansion of content.
We don’t create sites for search engines, we create sites for people. Balancing the needs of a spider with the needs of your visitor is a critical distinction.
While SEO (and IA for that matter) is not necessarily about design, a deep understanding of usability and interface design principles, with empirical data from testing, will pay large dividends (read: cold hard cash) from improvements in relevance, conversion rates and meritocratic sharing by site visitors. It’s all tied together.