The city is the World Wide Web, the buildings are its websites and the architects are the people overseeing their construction. As anyone who trawls the web will know, many sites are a nightmare to use - which means they are not doing the job they should be. Now, with budgets tightening, the pressure is on to make them more effective - without investing another fortune.

Navigation is the obvious area with which to start. Unlike most aspects of the web, it is closer to a science than an art. It is possible to say, with some objectivity, whether a site's navigation works or not. That does not mean there is only one "right" type of navigation. The only universal rule is that whatever you do, do it well. Broken links, links that go to the wrong page - these are unambiguous errors that give a poor impression. Beyond this, absolute judgments are off. Commercial websites have one or more jobs to do, and the appropriate navigation will vary.

If you have a site that is designed to build a brand, you will want to "trap" people on it for as long as possible. The navigation should keep visitors circulating within the site, moving them from one intriguing area to another - the longer visitors stay, the longer they spend absorbing the brand. The website of UK-owned brewers Guinness (www.guinness.com) is a good example of a site that encourages aimless clicking. If your site is informational - maybe it is a central corporate, publishing or government site - again you want visitors to stay as long as possible but you do not want to confuse them.

These are the sites where common sense rules are sufficient. Minimise the number of clicks between any two pages. Make sure users can always get back to the homepage quickly and easily. Keep the site coherent as it grows. Offer a search engine and a site map. See the Israeli Ministry of Foreign Affairs (www.mfa.gov.il) for a spectacular array of search options.

The third type of site is designed to help the visitor complete a task, or tasks. This could be any number of things: buying something, finding out about a product, checking a share price, looking for a job, whatever. Pretty much every corporate and e-commerce site falls into this category. It is also the one where most navigational mistakes are made.

The web is not a linear medium - there is no beginning, middle or end. This, it is often claimed, is terrific because it means the customer is in charge - he can go wherever he wants, whenever he wants. But why is it terrific? If customers in a supermarket wandered around all day without ever getting to the checkout, neither they nor the company would be very happy.

Online, this happens all the time: an alarming proportion of "shopping carts" is abandoned before customers get to the paying point. The aim of most commercial sites should be to convert a non-linear medium into a linear one - to create a journey, or series of journeys, that allows the customer to complete his task as quickly as possible.

We have identified two questions that most often break the linear journey:

• Does the user know which link to click on? Does it have a woolly label (eg "solutions")? Could users reasonably click on more than one link?

• Is the user being diverted? Few sites can resist the temptation of offering extra links on a journey. This is like tempting someone down country lanes while he is bowling down the highway.

For one thing, the "global site structure" link does not appear on every page - the centre is clearly not powerful enough to enforce it. For another, each department of ICI has come up with its own online design and layout.

The investor relations people, for example, have put their menu bar on the right. The press office staff, on the other hand, place theirs on the left. Some departments have a link back to the global homepage; others (such as ICI Schools) do not.

There are also huge variations in design (some sections are blocky and blue, some are elegant and white). This further hinders users' chances of orientating themselves.

Other little glitches can lead to big navigation headaches. Link to a section from the homepage, for example, and it appears in another window on your screen. Fine, but link back to the homepage and it appears in the same window, leaving you with two identical homepages. Annoying and confusing.

Logis de France
www.logis-de-france.fr

Some websites cater for lots of different needs and therefore offer lots of different services: press releases, news, product information, online entertainment, investor relations, job applications and so on. For these sites, a flexible navigation system, where a variety of avenues are always open to the user, is key.

But other sites serve just one specific purpose and good navigation here means a clear linear journey. Logis de France's site exists to allow visitors to find and book hotels and restaurants.

Its journey is a very smooth one, with no distractions along the way: Home page -> click -> map of French regions -> click -> map of Limousin -> click -> map of Corrze -> click -> map of a section of Corrze -> click -> list of local hotels -> click -> details of chosen hotel -> click -> reservation form -> turn gas off -> go on holiday.

Design? Very basic - bordering on the ugly, even. But layout is clean, links are intuitive and the journey from A to B is fast and effective.

Email David Bowen at dbowen@netprofit.co.uk and Scott Payton spayton@netprofit.co.uk