When dealing with scale on a map, the most important number you should keep in mind is

A ratio or representative fraction (RF) indicates how many units on Earth's surface are equal to one unit on the map. It can be expressed as 1/100,000 or 1:100,000. In this example, 1 centimeter on the map could equal 100,000 centimeters (1 kilometer) on Earth. It could also mean that 1 inch on the map is equal to 100,000 inches on the real location (8,333 feet, 4 inches, or about 1.6 miles). Other common RFs include 1:63,360 (1 inch to 1 mile) and 1:1,000,000 (1 cm to 10 km).