GPS navigation, among many ways of obtaining position, is widely used due to easy access to various GPS receivers. Nowadays practically every yacht has such a receiver. It gives us position with ±10 meters accuracy, calculates distance, displays GMT (Greenwich Mean Time) etc. Modern receivers enable us to insert way points, calculate course between these way points - compensating for current and wind and also warn us when we go off the planned course. However GPS will not know that there are dangers on the planned course such as shoals, rocks, wrecks or even other vessels or yachts. For example, if we wanted to go on shortest way from Gdańsk to Stockholm, according to shortest course taken from GPS, we would end up somewhere on Jastarnia beach.
Therefore it is good to know different ways of navigating as well as to know how to read a chart (for those who do not know - at sea we say chart not map ).
When using GPS during our voyages it is worth to remember that it is just an electronic device that may fail in any moment, usually the most inconvenient one. During military operations such as the one in Kosowo, during NATO forces landing, GPS can be simply 'shut down' for commercial users. It is good to back up satellite navigation with other methods.

On yachts equipped with GPS, satellite navigation is usually main source of obtaining position due to it's accuracy and availability - we have position (Lat and Long) at every and all the time. GPS is also useful for measuring distances (trip) and provides us an accurate time. It is worth to say, that the only thing we need to do to plot position on chart is to read coordinates (Latitude and Longitude) from GPS screen. There is no need to draw bearings and distances as in terrestrial navigation, so when navigating with GPS we just plot positions on chart with proper intervals to make our way safe. Next to every position we mark time and distance sailed (trip / log). However it is good practice to back up one method of navigation with other. Good navigator should know at least few methods if not all. One of the most important is terrestrial navigation, needed to verify that we really are in position GPS gave us.

One of the things to remember is to set proper reference coordinate system in our GPS receiver. Usually it will be most common WGS 84, but sometimes charts we use refer to other coordinate system and then we need to make a proper change in our GPS receiver. To understand what coordinate system or reference datum is please refer to: http://en.wikipedia.org/wiki/WGS84.

In terrestrial navigation position is fixed using navigational marks such as lighthouses, beacons, buoys etc., identified and compared to 'real world' by means of charts and other publications like List of Lights and Fog Signals, Sailing Directions etc. Once we have GPS position on chart and for example Lighthouse in our vicinity, it is good to go up on deck and check if we can really see that particular lighthouse. There is plenty of things we can do to counter check GPS. During the day we can simply compare shore line with description taken from above mentioned Sailing Directions (publication with detailed description of certain area, it's shore line, harbours etc), check if echo sounder is showing the same depth as the one on chart in our GPS position or , once we know how to do it, take bearings to lighthouse, beacon etc and obtain fix (observed position). Finally, more on ocean voyages, we can refer to stars and by means of celestial navigation calculate our position.

There is one fragment of book "Second time around the world" by Krzysztof Baranowski that comes to my mind when speaking about GPS:

Surely, this inaccuracy is not so important when we are at deep sea, but it becomes crucial close to shore or when approaching harbour (especially at night).