In a situation where you are forced to find your way across unknown terrain, a compass can be beyond useful. With its directional capabilities, the guesswork of which way you are going can be eliminated, giving you more precise directional clarity. While cardinal points are useful as well, being in a situation where you cannot find them may force you to rely on a compass. The alternative is to stay lost or get even more off course than you may have already been, neither of which is conducive to survival if supplies are running low or nightfall is looming.
Compasses have become extremely readily available in recent times. All sorts of bracelets and key chains are adorned with them. These are small, cheap varieties that are could be quite likely to break easily, however. Cell phones may also have the same directional capabilities, but that is only of use to you if your phone is charged up and working. Vehicles, too, have compasses, but again, that will only be of help to you if you are traveling in a vehicle. Otherwise you are going to need a portable compass to get you through, and there are three types from which you can choose.
A popular choice is the simple compact compass, which is the type of compass used in the bracelets and key chains mentioned above. While often low in quality of craftsmanship, the point of this compass is having something small and convenient to carry. This compass is able to give you a general guide as to which direction you are taking, but it is no frills and doesn't do anything special. If you are trying to plot a very specific course, this may not be the best compass for you, whereas if your course is more general in direction, it will get you there just fine.
Map compasses have much more going for them in terms of precise directional calculation. Since this type of compass is intended to work with a map, the base is often transparent so that you can look down through the compass and see the map below. While not the best for pocket carry due to sometimes bulky angles, this compass will fit into a pouch or pack or can be hung from a lanyard around your neck for easy access and continued use.
A lensatic compass is more of a heavy duty compass with a tough, durable frame containing it and a solid piece of plastic that protects the compass itself. In addition to being hard to damage, it can also be hard to carry due to its bulk and larger size. This type of compass can be utilized in low light scenarios and can calculate the exact bearing of an object. The benefits of this compass also come at a higher price than other compasses, but if you expect to be in a situation where details matter, this compass could prove to be a worthwhile investment.
Ultimately the compass you choose is going to need to reflect your needs and for what it will be used. In the categories above are many different designs and models of compass so you might be surprised what is out there when you start shopping around. Before you buy, do yourself a favor and remember that although you may only use a compass once in a blue moon, you will have to have it on you in order to use it, which can mean carrying something big at all times. If that is practical for you, then by all means go for it, but the decision may have to be made if it is worth sacrificing the carrying of something important to you in order to accommodate a large, cumbersome compass.