Legacy Maemo 5 Documentation/Human Interface Guidelines/Device Orientation
Device Orientation
Hildon is optimized for full functionality with Landscape screen orientation. Although both orientations are supported, some framework level functionalities such as the status bar, are not available in Portrait mode.
The switch between orientation modes can be done by the Hildon framework transparently for the application developer. The only relevant decisions for application developers are whether to request the portrait orientation mode and which interface elements to use on it.
Portrait mode is intended for simplified, one-handed use. Functionality may, and should, be limited in this orientation. For example, a Now Playing message for a media application, a read view for a PDF reading application, or simplified call handle controls.