A 'Thoughtmap' explains why we think the way we think. A Thoughtmap is what we use to think with, in contrast of what we think about.
For example: you may think about a person, and ask yourself: is she my friend or not? You are then thinking about friendship. Which thoughtmaps are you using to think with about friendship? Your 'friendship' thougthmaps inform you how you relate to what a friend is. A person might be a friend because they 'make you feel good', or because 'you have the same opinions on important matters', or because 'they listened to you', or when you have enough evidence that 'they will always be there for you, in good times as in bad times', or...
Thoughtmaps are nearly pre-verbal structures out of which we construct our worldview. Our thoughtmaps define how the world works for us. They determine what we can perceive and what we can express.
Each person assembles a unique set of thoughtmaps for themselves as their best way to survive in the world. This is why different people faced with the same challenges and the same resources create wildly differing results.