If you dont need to look at a map to tell you where to go then you probably have a

If you don't need to 'look at a map' to tell you where to go then you probably have a mental map.

Explanation:

Once an individual gets acquainted with a certain place, the features, landmarks, significant spots, roads, etc. of the place become familiar to him. His brain has a navigational map automatically generated of the places that are familiar to him. This kind of map that is formed in one's brain is called a 'Mental Map'.

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