Most standalone GPS units have a night mode that draws the map with dark colours so the glare doesn't distract you while driving, but many smartphone GPS apps lack this critical feature. However, you can give any GPS app a reasonable stand-in for a real night mode by inverting your phone's screen.
We've previously suggested inverting your screen for easier reading at night, but it occurred to me while driving recently that the same trick works well for nighttime navigation.
On an iPhone, go to Settings > General > Accessibility, then set your Triple-Click option to invert colours (not while you're driving, please). Then, you can triple click your home button at any time to invert the screen. Hopefully Google and Apple will update their iOS mapping apps with real night modes, but until then, this is a decent hack to keep the glare out of your eyes.
Google was kind enough to include a night mode in Google Maps for Android, but if you're using a third- party app, inverting your screen isn't quite so simple. Stock Android doesn't offer a system-wide inverted mode, but a lot of custom ROMs do. No matter your platform though, having a bright white screen in the corner of your vision isn't safe when you're driving at night, so anything you can do to dim it is worth the effort.