Placement of the horizon is important to the success of every photograph. A poorly placed one or one that isn't level certainly detracts from the impact of the picture. To make sure you capture one properly, use a bubble level that fits into the hot shoe of the camera. Some tripods have bubble levels built in. My camera has on-demand grid lines, so I can line up the horizon with one of the horizontal lines of the grid. Many newer cameras have levels that can be displayed on the LCD—check your manual to see if you have this feature. Where the horizon is positioned is determined by a number of factors. Let's examine some of them.
1) EMPHASIZE FOREGROUND: When I photograph the landscape, my eye is constantly on the lookout for ways to make a foreground, middle ground and background come together. More often than not, this means including as little sky as possible. The reason is, I want the elements of the land to be the dominant features. By excluding the sky, the horizon naturally falls off-center and is usually in the top 25 percent of the composition. In the first image made at the Racetrack in Death Valley, I wanted to emphasize the eroded line the rock made across the bentonite playa. To establish a sense of place, I included the mountains in the background. The horizon is implied where the playa and mountain meet.
2) EMPHASIZE SKY: If the sky is on fire, or if the clouds are interesting, or if what's going on above the horizon is more intriguing than what's below, this is the time to emphasize it. As a matter of fact, if the sky conditions are electric, a skyscape may be the best choice. When it looks as if the conditions are right for a great sunrise or sunset, it's essential to look for an interesting foreground to anchor the show above. Dramatic color doesn't last long, so work fast to garner as many images as possible. Given the foreground you choose, make verticals and horizontals to capture the diversity of the scene.
3)REFLECTIONS: You've probably heard the compositional rule that an image with a centrally placed horizon is a mistake. As it's true in many circumstances, I have to disagree with it when it comes to reflections. By definition, a reflection creates a mirror image that results in a 50/50 split of the subject matter—50 percent of the actual formation and 50 percent of it reflected. This creates a logical split where the horizon needs to be dead center. So, although there are guidelines and rules, there are also times when they can be broken.