GPS navigation
Satellite navigators, such as GPS devices use satellites to get your position. They can often be equipped with maps and be told your intended route or calculate routes to your destination.
GPS has been used by boaters and hikers for many years, but, more recently, devices that include road maps have made GPS a convenient way to navigate roads by car or on foot. Standalone GPS navigation devices can be purchased for about $100, and smartphones usually include GPS navigation as part of the standard suite of applications. Additional navigation apps can be downloaded. Some navigation apps allow maps to be downloaded and stored on a phone. These are particularly useful to domestic travelers in areas with poor mobile data and international travelers who do not want to pay for data service while traveling.
If you are traveling more than 50 miles/80 km with the device turned off, it can take about 20 to 30 minutes to re-align with the GPS satellites. Be sure to turn it back on as soon as you arrive, so you won't have to wait when it's needed. Some makes such as TomTom offer a weekly internet download to shorten to startup time when the device is first turned on for the day. This is good for normal everyday use, and will save about minute. However, it won't help at all if you've traveled too far with the device turned off.
If you already own a smartphone, the built in apps can save money over buying a standalone GPS device or renting one from a car rental company. They may also give more features, and quicker fixes when working with phone signals. When out of range, however, their performance is sometimes poor. They usually have a less suitable user interface for driving.
Some apps allow download of maps to a smartphone's memory card before departure, avoiding the need to consume expensive data on mobile telephone networks while moving. Android is slightly preferable to Apple in this regard as additional flash memory can be added by purchasing "micro SD" cards for the device.
The availability of turn-by-turn directions varies between apps and may not be included in some free applications.
HERE (formerly Nokia Maps)
Free app for Android, iOS, Windows Phone/Windows 10 Mobile. Also available through their website. Offers turn by turn navigation and offline maps for about 120 countries. Translated to about 25 languages. Includes walking navigation and public transit navigation (in some areas). Uses HERE's own maps with the ability to improve the maps by the general public via HERE's map creator.
CoPilot GPS
One country map can be downloaded for free and used with restricted functions. Additional maps can be purchased after an upgrade to voice turn by turn navigation for $24.99.
Brazil, Australia, New Zealand, US, Canada, UK, Ireland, Balkans, BeNeLux, Russia, Central Eastern Europe, DACH, France, Greece, Iberia, Italy, Nordics, Poland, Romania, Turkey, Ukraine, South Africa, Lesotho, Swaziland, Namibia and Botswana. Middle East Maps (Bahrain, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, UAE).
MAPS.ME
Free on Google Play and iOS App Store, MAPS.ME allows download of all or part of the OpenStreetMap (OSM) world map (selectable per-province or per-country) to an Android's flash memory card. Downloading the entire world is huge, so only viable if you have a large MicroSD card on your Android as extra storage.
OsmAnd
Available Google Play and iOS App Store. Maps from OpenStreetMap (OSM).
Free application with maps from OSM.
Andorra, Argentina, Australia, Austria, Benelux (Belgium, Netherlands, Luxembourg), Brazil, Canada, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, India, Ireland, Italy, Latvia, Lithuania, Mexico, Monaco, Netherlands, New Zealand, Norway, Poland, Portugal, Slovakia, Slovenia, South Africa, Spain, Sweden, Switzerland, UK.
Issues
Although a GPS navigator makes navigation and orientation very much easier in many situations, it is no silver bullet. In some circumstances the information given by the device may be misleading. Some navigation or orienteering skill and some experience with the device will be needed to identify and handle these situations. And like all electronics, the device can fail, and (you know Murphy, don't you!) it may fail at the worse possible moment.
Not all maps are accurate, reliable and up to date. Whether they are is often difficult to know without local experience (most map makers will at most promise best effort). A road or fairway being on the GPS map does not guarantee that the road is usable or that the real-life fairway is at exactly that position.
Especially paper maps may use coordinate systems other than WGS84 (which is used by the GPS), thus giving a mismatch in positions unless correction data are used. Check beforehand. If you're in England, France, or Spain, don't forget to double check east (+) and west (-) longitude coordinates, as these countries have both.
There are circumstances where the devices do not work well and some devices have quirks. A device (or app) meant for driving may place you at any nearby road, even when walking or sailing. The position, although mostly accurate, may sometimes be quite much off also for other reasons. In dense forests, heavy rain etcetera the device may not find the satellites. Most devices have a lag, which may be confusing at tight turns.
Some manufacturers (such as Garmin) market specialised devices specifically for marine use. The underlying satellite signal is the same, but a marine GPS stores nautical charts (usually purchased separately) instead of highway maps. If you take this on the autobahn, it'll display valid co-ordinates but tell you that you've run aground.
The device should be usable for the intended use. A device used by the driver should allow him or her to concentrate on the driving. A device used outdoors should be rain and moisture resistant. The controls should be usable also in the field and the display bright enough in sunshine and dim enough in the night.
The device may fail. You should have some backup, usually including paper maps and paper notes about where you are, including time of and direction since last update (depending on circumstances, good mental notes may be enough).
You should evaluate the route suggested by the device. When orienteering, the shortest route is hardly ever appropriate, so you should be able to find your way between (and choose) waypoints in the traditional way. When driving, the "shortest route" may be nice, but may also be blocked or unusable. The "fastest route" is more reliable, but may still be blocked by e.g. roadworks. And the GPS with turn-by-turn directions cannot know that the sneaky shortcut directly across the main runway of a major airport is a bad idea, if the mapmaker carelessly omitted a locked gate or two. While boating, remember that boats, swimmers, birds and that half-submerged log are not on your map.
Don't drive a double-decker bus under a low bridge just because a car GPS says this is a fine route. Maps intended for large trucks and lorries indicate low-clearance underpasses or similar restrictions that are simply not on a standard map built into a small motorcar GPS.
In most cases, the screen is small and resolution not as good as on paper. This is a tradeoff between resolution and portability; a laptop PC with a USB GPS receiver would display more detail, but is bulky and power-hungry enough that it's rarely used in this application. You may have to use paper maps to get an overall picture of your route, both while planning and every now and then. Zooming on the device helps only little, as you need more details than you will get when zooming out.
Satellite navigation uses quite a lot of power. This is seldom an issue while driving (unless you forgot the power supply), but may be a serious problem when wilderness backpacking.
Alternatives
There are a number of satellite navigation systems other than GPS though, as of mid-2014, none of the others are as fully developed or as widespread. Some governments are quite averse to the idea of having anything important depend on GPS, because the US government controls the GPS satellites and could manipulate the service for political ends.
Already China, India and Japan each have a regional system that covers part of the world, while Russia has a worldwide system in operation. The European Union's Galileo and China's BeiDou are both expected to provide worldwide coverage by 2020.