Has anyone noticed that with the iPad, Douglas Adams’ fantasy has come true?

The late Douglas Adams, in his bestseller The Hitchhiker’s Guide to the Galaxy (conceived in 1971 and published in 1979), introduced the idea of a handy travel guide that looked “rather like a largish electronic calculator,” with a hundred tiny flat press buttons and a screen “on which any one of a million ‘pages’ could be summoned at a moment’s notice. It looked insanely complicated, and this is one of the reasons why the snug plastic cover it fitted into had the words DON’T PANIC printed on it in large friendly letters.” According to Adams, this guide was published in this form because “if it were printed in normal book form, an interstellar hitchhiker would require several inconveniently large buildings to carry it around in.”

The iPad fits the description, except that it doesn’t look insanely complicated. Its sexiness and sleek design is a triumph of style over function. It’s a powerful experience to hold full Web or e-book pages in your hands in a device that weighs little more than a thick magazine. But the iPad experience also includes knowing where you are, changing the display depending on how you hold or rotate it, and responding to multiple-finger touches and gestures.

The only insanely complicated part of the iPad is trying to develop a killer app that best exemplifies the iPad experience.

Rethink Your App Design

If you’ve developed applications for a desktop or laptop, or even for an iPhone or iPod touch, you have to rethink your design for the iPad. For many iPhone app developers, the iPad’s larger display alone changes everything. Apple demonstrated exactly how far things have changed when the company demonstrated the iWork suite of productivity tools (Keynote for presentations, Numbers for spreadsheets, and Pages for word processing and page formatting) on the iPad, which would be unthinkable for the iPhone simply because there isn’t enough display space to perform functions such as slide or page layout. The iPad allows both immediacy and intimacy as it blends mobility and the power of the desktop to create a new kind of freedom. It lets you develop a totally new kind of application — one that integrates seamlessly with what the user is doing when he or she is living in the real world.

Douglas Adams, in his own inimitable style, wrote about sexiness and how it can make a product more popular. According to Adams, The Encyclopedia Galactica describes alcohol as “a colorless volatile liquid formed by the fermentation of sugars” and also notes “its intoxicating effect on certain carbon-based life forms.” On the other hand, The Hitchhiker’s Guide to the Galaxy not only tells you what alcohol is, it also tells you that “the best drink in existence is the Pan Galactic Gargle Blaster,” describes its effect as “like having your brains smashed out by a slice of lemon wrapped round a large gold brick,” tells you which planets have bars that offer it and at what prices, and then shows you how to mix one yourself. As Adams points out, “The Hitchhiker’s Guide to the Galaxy sells rather better than The Encyclopedia Galactica.”

Simply converting an iPhone app (or even worse, an app for a Windows netbook or other smartphone) may result in something like The Encyclopedia Galactica —nowhere near as sexy as it should be. You can create iPad apps that are not just a little bit better than their iPhone counterparts, but a lot better (and an order of magnitude more powerful), with an interface that’s simpler to use than a Mac.

Provide an Immersive Experience

An iPad app can offer a more immersive experience compared with an iPhone app by adding more content — full pages from the Internet or in memory, maps you can zoom into, full-screen videos and slideshows with music, and so on. Whenever possible, add a realistic, physical dimension. Electronic Arts created a version of its popular car-racing game Need for Speed for the iPad that almost feels like you’re driving with your hands as you use the iPad like a steering wheel. The high-definition screen is just inches from your face — the field of view and the sensation of speed you get is incredible. The full-screen display is also fully touch sensitive — you can tap on a car and see inside it, flick a lifelike gear shifter to shift gears, and tap the rear-view mirror to look behind you.

The more true to life your app looks and behaves, the easier it is for people to understand how it works and the more they enjoy using it. E-books look like real books, and you can even turn a page with a flick of the finger. The New York Times app for the iPad app offers an immersive experience with what looks like a newspaper, with embedded, fully functional videos (not just videos that appear in a separate window). You can tap the page to change the layout of columns, resize the text with a pinch, or show pop-up menus for more stories. These are very basic features, and if you’re designing an e-newspaper for the iPad, you will have to think beyond them — to advertisements that pop up and engage the reader in novel ways, and social connections for sharing stories, photos, and videos with others.

Make Content Relevant

An iPad app can present information relevant to where you are, what time it is, what your next activity might be, and how you’re holding the device (in portrait or landscape view, tilting and shaking it, and so on), just like an iPhone or iPod touch app. For example, the version of Maps for the iPad displays a full-screen map that can show your location and immediately find commercial establishments nearby (you can search for “sushi” to find sushi restaurants). As people move, it may make sense for your app to tailor itself to where the user is, moment by moment.

The iPad platform also offers a strong foundation for controlling views, managing data, playing multimedia content, switching display orientations, and processing gestures. Because the iPad can do all that, an app can know your current location, the hotels or campgrounds you’re going to stay at, and the planets you’re planning to visit. It can even show videos and play the music of the stars all at the same time. Rather than orbiting some moon while searching maps and brochures, you can know at a glance where you are, how to get to your destination, and what the weather’s like so that you know what to wear.

As a developer, you need to consider the context of what the user is doing and the user’s location, and provide as much content as possible that is relevant for that user in that location. For example, your app can show a special keyboard unique to the task, such as the numbers-and-formulas keyboard that appears in the Numbers app for the iPad. Your app could help the user grab and use personal content from Apple’s supplied apps (such as Contacts and Photos). And with the Internet always available (within reach of Wi-Fi or 3G), your app can provide real-time information. This kind of access also allows you, as the developer, to go beyond the limited memory and processing power of the device and access large amounts of data stored on servers, or even offload the processing. You don’t need all the information for every city in the world stored on your iPad for your travel app — you can send the request to a server for all that information, especially information that changes often.

Design for Touch

The important design decision to make, whether you’re starting from scratch with a new iPad app or evolving one from an iPhone app, is to use the iPad display and user interface elements to give people access to more information in one place. Although you don’t want to pack too much information into one view, you also want to prevent people from feeling that they must visit many different views to find what they want. An iPad app can offer the primary content on the main view and provide additional information or tools in an auxiliary view (such as a popover that appears semi-transparently above the main view) to give users access to functions without requiring them to leave the context of the main view.

The iPad display also gives you a lot more room for multifinger gestures, including gestures made by more than one person. An iPad app can react to gestures and offer touch controls and pop-up settings that are relevant to what you’re actually doing in the app and where you place your fingers. With a display the size of a netbook, you have a lot more screen real estate to allow dragging and two-finger gestures with graphics and images, and depending on what you’re doing, a tap or gesture on a particular part of the screen can have a particular function. For example, in the Gameloft version of the first-person shooter called Nova (as adapted to the iPad), the display size gives you more flexibility than the iPhone version, with more controls and objects such as mini-maps, and you can slide two fingers across the screen to throw grenades. If you design an app that simply uses a single finger tap as if it were a mouse click, you may be missing an opportunity to design a better user experience.

Keep Apple’s Expectations in Mind

Just as the iPad can extend the reach of the user, the device possibilities and the development environment can extend your reach as a developer. It helps to understand Apple’s perspective on what iPad apps should be — the company clearly has done some serious thinking about it.

So what does Apple think? Spokespeople often talk about three different application styles:

• Productivity applications use and manipulate information. Bento (FileMaker) is an example, as are Apple’s iWorks apps — Keynote, Pages, and Numbers. Common to all these apps is the use and manipulation of multiple types of information. (I’m not talking about the Productivity category in the App Store — that’s a marketing designation.)
• Utility applications perform simple, highly defined tasks. The preinstalled Weather app is an example — it deals only with the weather data. The Brushes app for painting (Steve Sprang) is considered a utility, as it performs a simple, highly defined task. (Again, I’m not talking about the Utilities category in the App Store, although many of those apps are considered utility apps because they perform simple, highly defined tasks.)
• Immersive applications are focused on delivering — and having the user interact with — content in a visually rich environment. A game is a typical example of an immersive application.

These categories help you understand how Apple thinks about iPad apps (at least publicly). Pay attention to what Apple thinks. To make you development effort pay off, you need to spend time upfront understanding the iPad user experience, how applications work in the iPad environment, and the guidelines that Apple enforces for apps to be approved for the App Store. You also need some marketing advice to keep your app from being insignificant in the vast galaxy of apps. For the App Store is like space itself, and as Douglas Adams notes, space is “big, really big . . . you just won’t believe how vastly hugely mind-bogglingly big it is,” and suggests that you bring a towel.

The next installment gets into a bit more detail about exploiting the iPad platform features and embracing its limitations, and the third provides tips on avoiding the Apple rejection slip.