Principles of Good Interface and Screen Design 291

Step 3: Principles of Good Interface and Screen Design 291

Page printing: — Provide a means to print

• Groups of related pages. • Individual pages. • Sections of pages.

Maintainability: — Ensure easy Web site maintainability.

Downloading. Slow download speeds are an ongoing complaint of Web users.

Download times of 8 to 10 seconds per page should not be exceeded, even for bandwidths of 28.8 Kbps. In general, keep graphics and page size as small as pos- sible. Specifically, use text instead of graphics whenever possible. When graphics are desirable, keep the graphic as small as possible. Also, repeatedly use a graphic so it may be stored in the browser’s cache.

The cache is a temporary storage area for Web pages and images. There are two types: memory and hard drive. Once a graphic is downloaded, it is placed in the cache and remains there for a prescribed period of time. Download times, then, are longest when a site is visited and downloaded for the first time. After the first download, the graphic is in the cache. It is retrieved from there, reducing the time it takes to display the page.

In addition to graphics, other design elements that slow download times include large and chunky headings, the use of many colors, animation, excessive use of frames, and the use of Java and JavaScript. Limit the use of these elements that require a long time to download. Create graphics that load quickly. Limit an individual image to 5KB, the images on a page to 20KB. Use Graphics Interchange Format (GIF) files because they are smaller than Joint Photographic Experts Group (JPEG) files. GIFs and JPEGs are described in more detail in Step 11.

Also, because few monitors display images at greater than 72 dpi, restrict the resolution of downloaded images to 72 dpi. Using a higher dpi ratio will not pro- duce a better image, but will increase file size, causing longer download times. All images should also contain alternate text (alt text). This will give the user something to read while the image downloads, and is necessary for text-only viewers.

Always provide enough information to let the users know whether it is worth their time and trouble to download something of apparent interest described on

a Web page. Provide a program or document description, type, size, version, esti- mated loading time, and any special operating requirements, including such things as hardware needed, the required operating system, special software needed, and memory requirements.

Currency. Update the Web site regularly to keep information current. The nature of

the Web implies timeliness. Outdated information casts doubts on a Web site’s credibility. Currency means trustworthiness to many users.

292 Part 2: The User Interface Design Process

Page Printing. Some people prefer to read hard copy, especially anything longer than half a page. Make printing easy for users, including the capability to print sections, pages, or groups of related pages with minimal effort. Since most low- end printers print at 300 dpi, pages may be printed at this resolution. This higher resolution will result in a longer printing time, however.

Maintainability. Provide easy Web site maintainability to sustain its currency. Change must be easily accommodated as the Web site grows, evolves, and matures. Web site maintenance is, in reality, Web site enhancement. Remove out- dated information and expired links, link old pages to those newly created. Properly designed, modular system pages covering specific topics can be updated quickly without needing to change and reformat large amounts of information.