Narrow gauge refers to any railway track where the distance between the inside edges of the rails is less than the international "standard gauge" of 1,435 mm (4 ft 8.5 in). Most narrow-gauge systems worldwide range between 600 mm (1 ft 11.6 in) and 1,067 mm (3 ft 6 in). These systems are historically popular in mountainous or difficult terrain because they allow for tighter curves and smaller tunnels, significantly reducing construction costs. Famous examples include the Disneyland Railroad (3 ft gauge) and the extensive 3 ft 6 in networks in Japan, New Zealand, and South Africa. While they are more cost-effective and charming, narrow-gauge trains are generally limited to lower speeds and have reduced stability compared to standard or broad-gauge trains, which is why they are often used today for heritage lines, industrial mining, or regional transit in geographically challenging areas.