Explain the degree to which physical features have contributed to the distribution of languages.

Most topographic maps, the index contour lines are generally darker and are marked with their elevations. 

Each meridian forms half of a great circle, assuming a spherical earth. meridians intersect lines of latitude (parallels) at right angles. the spherical earth is divided into  360 degrees   east-west. lines of longitude range from 0° to  180° to the east and from 0° to -180 ° to the west of the prime meridian.