Theory:

Legend:
The legend of a map helps to understand the map details which are placed at the left or right corner at the bottom of the map.
A legend in general consists of all the symbols used in a map. These symbols are commonly used to describe different features mapped. For example, cities or airports are commonly represented as point symbols (depending on scale), roads or railroads are usually represented by line symbols, and the cities, lakes, or forests are common examples of region symbols.
Example:
4.png
The above-shown map has used various symbols to represent the highways, roads, population index etc.,
Scale
A scale is a ratio between the actual distance on the map to the actual distance on the ground.
Real-world features can't be drawn on the map as large as their true size. Therefore to represent the real world, maps are made to a specific scale.
Example:
5.png
 
The above image of a scale shows various ways of representing a scale.
  • a) is the Verbal scale.
  • b) is the Representative Fraction (RF) or Fractional scale or Ratio scale.
  • c) is the Bar scale or Graphic scale or Linear scale.
Analysing a grid map
5.png
 
From the verbal scale given above, it is clearly understood that \(1\) unit is equal to \(250m\). Therefore, each square block in the scale's respective map is of \(250m\). Hence, while calculating the distances (both possible and shortest routes), the scale must be considered and calculated simultaneously.