Web site architecture, like the architecture of a house is incredibly important, it's truly, the structure upon which your website is built. It may not seem important and it's certainly not sexy, like headers and opt-in lists but in the long term, I believe that site architecture is, after the text, the next most important component of the average site.

Why?

Well, there are three reasons:

1   Being unable to find information where it should logically be e.g. I visit a home produce site and I find that in the growing citrus trees section there are pages for:

• lemon trees
• lime trees
• orange trees
• cumquat trees   

...but no INFO on mandarin trees. It would be unfortunate for the site owner if he had arbitrarily decided to incorporate mandarin trees into the orange trees section because of the similarity of their needs. The logic of the site architecture indicates that mandarin trees would have their own page if they were being covered and the website might be losing valuable traffic because of this haphazard approach to site architecture.

2   As a website visitor, it can be incredibly frustrating to get lost in a site. This is a disaster, undoing much of the good you may have already created and probably resulting in your visitor angriily clicking out of your site.    

3    This point is really only a continuation of the point above but it's from the search engines' perspective. If your website architecture doesn't have a logical progression of ideas and there are dead-ends or dead links, the search engine spiders devalue your site and there is a very good possibility that your ranking will decrease (or never increase) because of that.  

I'm sure that many of you will assume that all websites are created with  a logical site architecture but that just isn't the case. Many websites may start that way but as the site grows, a sprawling menu is created that digs only 1 or 2 levels from the home page   

e.g. let's say you have a hardware store and you sold a number  of brands of hammers, your navigation for Brill's Hammers (a brand that I've made up) might well look like this:

     HomeHammersBrills Hammers

You can imagine that there'd be numerous links off the homepage for:

• screwdrivers
• nails
• chisels

...etc., which would be fine if it was a small site but if it grew to incorporate:

• gardening supplies
• outdoor weather clothes etc.

...that homepage could start to get chaotic. If you can pre-design your site to incorporate site architecture such as:

    HomeBuilding ToolsHammersBrills Hammers

    HomeGardening supplies

    HomeOutdoor weather clothes

a  your web designer hours will be greatly cut (meaning you'll get a better deal)

b  you'll know exactly what's supposed to be on every page &

c  your surfers will stay at your site and won't click away in frustration. Though it's from 2002, this article, from the prestigious Jacob Nielsen's Alertbox, states in paragraph 3:

N.B.: If Brill's Hammers had an accessory, like special gloves, you'd have to make a decision as to whether Brill's Hammers Special Gloves were in   

• Building ToolsAccessories
• HammersAccessories
• Brills HammersAccessories or
• HammersSpecial gloves

...and in that case, any of them might be appropriate.

Probably the best approach might be to split-test the appropriate page over a few weeks (index in seasonal changes, natural disasters etc. if needed), and see which placement gets the most sales! 

Thinking about your website architecture in this simple, logical way, will enable you to help both your customers and the search engines. Google's unofficial spokesman, Matt Cutts, confirms this at his July 2006 videoblog: Matt Cutts on web site architecture (1.20-2.20).