PHYSICAL GEOGRAPHY GPH111
LAB F - INTRODUCTION TO GEOGRAPHIC TOOLS - CONTOUR LINES
AND PROFILES
Introduction
Topographic maps are distinguished by their ability to show elevation relationships with contour
lines. The brown lines on a topographic map are contour lines, lines representing an
imaginary line on the ground along which all points are at the same elevation. Contour lines
also show the shape of features on the terrain. Given a series of surveyed data points and their
elevations, one can construct a contour map of any known surface. In this exercise the student
will become familiar with contour lines and their characteristics. Students will also use an
enlarged section of the Folsom, New Mexico Quadrangle to “interpret the language of the
contours”, to determine elevations, types of slope and features (landforms) on the map. Lastly,
students will construct a contour profile, or cross section diagram, of a selected map section
Materials needed: pencil, Buffalo Head enlarged section + 2 topographic maps (on reserve)
Part I. Characteristics of Contour Lines
Before beginning, review the following rules or characteristics concerning contour lines.
1. Closely spaced contour lines indicate a steep slope (Figure F-1).
2. Widely spaced contour lines indicate a gentle slope (Figure F-2).
3. Evenly spaced contour lines indicate a uniform slope (Figure F-2), while irregular spacing
indicates an irregular slope (Figure F-1).
4. Contour lines that are widely spaced at the top of the slope and closely spaced at the
bottom of the slope depict a convex slope. Contour lines that are closely spaced at the top
of the slope and widely spaced at the bottom depict a concave slope.
5. Contour lines may lie very close together, may even appear to coalesce. Such lines
indicate a very steep slope or cliff; however, contour lines never cross, merge, touch,
branch or fork.
6. Completely closed contour lines indicate tops of hills, mountains, peaks etc. These
contours would indicate higher elevation than the surrounding area in all directions (Figure
F-3).
7. Bent contour lines indicate a rise in elevation (spur or ridge), or a drop in elevation (valley)
An example of a valley is shown at (Figure F-4).
8. Lines depicting a valley bend up-valley, toward the higher elevation (Figure F-4).
9. Hachure marks within contour lines indicate a significant, closed depression (Figure F-5).
10. Brown is the color used by cartographers for most contour lines. Light brown is used for
intermediate contour lines. Every 4th or 5th contour line (depending on the contour interval)
is an index contour line, is a darker shade of brown and labeled with the appropriate
elevation (Figures F-4, F-5 or F-6). Index contour lines speed the process of interpretation.
11. The vertical distance between adjacent contour lines is known as the contour interval.
This contour interval is given in the marginal data of the map sheet. Unless otherwise
marked, points that lie between contour lines assume a value of one half of the contour
interval of the map.
F-1
