Pilotage is the use of fixed visual reference on the ground or sea by means of sight or radar to guide oneself to a destination, sometimes with the help of a map or nautical chart. People use pilotage for activities such as guiding vessels and aircraft, hiking and scuba diving. Pilotage techniques apply when close enough to land or other navigational reference points. In these circumstances there is often not enough time for more elaborate navigational techniques that are used when out of sight of both navigational aids and hazards. In these circumstances, it is usually not necessary to know exactly where you are, but that one is in a safe position, or at least on a safe line and will remain so for a period of time, and to know when the next change will be reguired Without such pilotage references, it is necessary to navigate using dead reckoning (typically with a compass and some form of log for speed or distance estimation), radar, radio navigation, and satellite navigation (such as (GPS)