The elevation difference between two adjacent contour lines is called the contour interval (CI). Usually the contour interval is noted on the map legend. In most topographic maps every 5th contour line is drawn in bold print or wider than other contours. Such lines are called index contour lines.Click to see full answer. Also, what 2 types of lines show elevation differences?Topographic maps have contour lines that connect points of identical elevation above sea level. Contour lines run next to each other. Adjacent contour lines are separated by a constant difference in elevation, usually noted on the map. Topographic maps have a horizontal scale to indicate horizontal distances. what is the change in elevation from one contour line to another? is the difference in elevation from one contour line to the next. For example, the contour interval on the map below is 10 feet. This means that the change in elevation between contour lines is always 10 feet. The contour interval can differ from map to map, but it is always the same on a particular map. Subsequently, question is, how can you identify the top of a hill or mountain from contour lines? Think of contour lines as the distance between each incline. The closer together the inclines, the steeper the hill. On the other hand, the farther apart lines tend to indicate a depression in the landscape. Another way to tell elevation is the numbers on the map.How do you read elevation?Run the detector and / or front rod section up or down until you pick up the “on grade” signal from your detector. Read the number opposite the pointer. That number is your true elevation. If using an optical instrument, just read the number across the horizontal line.