Range in geography typically has two meanings.
A range in geography is most commonly used to describe a series of adjoining hills or mountains, usually in a roughly linear manner. It is usually linear because it defines the boundary most commonly where two tectonic plates came together and caused massive uplift. Lesser examples of uplift can be from earthquakes or similar tectonic activity and cause smaller hill ranges or ridges.
There is also something called the range of light in geography. It is useful for ocean navigation, especially for an observer on a ship at sea trying to determine the distance to a light on the horizon, or, if you are building a new lighthouse or navigation aid, and you want to calculate how far out the light will be able to be seen to help you decide how high off the ground to build the light source. If you know your height above the water, anywhere from zero to infinity, you can calculate how far away the light will be seen. In reality, there is a quick look-up table most mariners use to do this, but you can also calculate it manually. The formula is: Distance to the Horizon in nautical miles (d) = the constant (1.17) multiplied by the square root of the height of the object in feet √h." The calculation should then be repeated for the observers Height of Eye and the results summed to obtain the Geographic Range of the Light.
