One application of trigonometry in the real world is determining the distance and location of faraway objects. This is useful in navigation and in surveying. Historically, trigonometry was also applied to determine the position of heavenly bodies, but this use has been supplanted by linear algebra in modern times.
Using trigonometry, it is possible to measure objects, no matter how large or inaccessible they are. Knowing the distance and angle between the observer and an object, the height of a tall object such as a cliff can be ascertained. The height is treated as one side of a triangle, while the distance between the observer and the top of the cliff is treated as another side of the same triangle. The problem of finding the height of a tall object is turned into a simple trigonometric calculation. The same method can be applied to objects lying along the plane of the Earth, such as a distant lake. This method is called triangulation and has a long history of application in navigation and map-making.