Aspect ratios for Digital Signs
Most modern screens have an aspect ratio of 16:9 (widescreen) although 4:3 monitors are still common and many computer monitors have slightly different ratios like 16:10. Some display manufacturers are starting to create novel displays with unusual aspect ratios like the LG M3800S-BN display which has a very wide format making it ideal to squeeze into a narrow space on a wall such as above a bar or cabinet. The most important thing is to ensure that your chosen display type and orientation is supported by your digital signage software so that it can create content that fills the display with no black bars and no distortion.
Most digital signage software also supports displays that have been rotated 90 degrees to the left or right. This can be a great way to maximize screen space on a narrow wall like in an entrance lobby. It also makes for a good poster format for content more suited to an arrangement like that, for example, a menu. But before you try mounting a display in a rotated configuration you should make sure it has good viewing angles in that orientation (more on that below).