The dimension of an array directly depends on the screen size of the device it is being viewed on. The jumping point is of course the iPhone. In many cases, match-three games are played in Portrait mode, so the width of the game board is equal to 320 points (640 pixels on the Retina display and 320 pixels on the iPhone 3GS). As long as touchscreen input is based on direct manipulations with objects on the screen, a game tile should be comfortable to aim and tap. (Systems with non-direct manipulation, which use buttons or a joystick to control the screen pointer, can use smaller tiles and more elements.)

As you remember from Chapter 2, Ergonomics, the optimal minimum size of a touch area is 44 pixels. If we divide 320 points by 44 points, the rounded-up result is 7.3. Hence the optimal number of elements is seven or eight; you can check this out for yourself by looking at any screenshot of the Bejeweled game, which utilizes eight items in a row. Besides the ergonomics issue, there is another important point: the visual quality. Small tiles can feature only simple graphics, tiny details and textures can be blurred, so try to connect the width of the array to your artwork (for example, another match-three game from PopCap Games named Chuzzle uses only six tiles in a row to express the visual look of game tiles better). Thus, the cornerstone principle is obvious: the simpler the design of the tiles, the more elements that can be placed in a row of the array. For instance, Bubble Explode (http://www.spookyhousestudios.com/bubbleexplode.html), a match-three puzzle from Spooky House Studios UG (haftungsbeschränkt), features game tiles with a very laconic and uniform design. They look like small color bubbles, so 10 items are easily placed a row:

Screenshots from various match-three games from Spooky House Studios UG (haftungsbeschränkt)