Using these charts and other tools, pilots are able to determine their position, safe altitude, best route to a destination, navigation aids along the way, alternative landing areas in case of an in-flight emergency, and other useful information such as radio frequencies and airspace boundaries.
When an aircraft is flying under instrument flight rules (IFR), the pilot will often have no visual reference to the ground, and must therefore rely on external (e.g. GPS or VOR) aids in order to navigate.
Only limited topographic information is found on IFR charts, although the minimum safe altitudes available on the routes are shown.
En-route low- and high-altitude charts are published with a scale that depends upon the density of navigation information required in the vicinity.
Terminal procedure publications such as standard terminal arrival plates, standard instrument departure plates and other documentation provide detailed information for arrival, departure and taxiing at each approved airport having instrument capabilities of some sort.