These maps are built in our heads. There are two sources of information in which we use to form mental maps. The first is direct perception of the environment in which we live. The second is the viewing of other maps that have been previously drawn. We all have a mental atlas of shapes of states and countries.
Mental maps are essential for use in everyday life.
We use our mental maps when we walk around campus to find where our next class is or when we are driving in the city. From 250 B.C. to 100 A.D. we see major accomplishments by Greek scholars in understanding how to represent the earth. Two individuals in particular contributed greatly to the development of Cartography, a field of study that deals with the mapping of the Earth. He then multiplied the distance between the two cities to arrive at an Earth's circumference of about 46,000 km. The actual measurement is 40,000 km, or 25,000 miles.