Chapter 2, section 4: Maps in Earth Science Vocabulary: 1. relief: variations in elevation of a land surface. 2. elevation: the height of an object above sea level. 3. topographic map: a representation of the surface features of Earth. 4. contour interval: the difference in elevation between one contour line and the next. 5. index contour: a darker, heavier contour line used to make a map easier to read. 6. geologic unit: a rock of a given type and age range. 7. contour lines: a line that connects points of equal elevation. They are normally are in brown. 8. geologic map: a map that shows the distribution of geologic features in a given area. The map shows rock units, mineral deposits, and fossil localities.