Elevation and Relief - Interpretation of Terrain Features
107. INTERPRETATION OF TERRAIN FEATURES
Terrain features do not normally stand alone. To better understand these when they are depicted on a map, you need to interpret them. You can interpret terrain features by using contour lines, the SOSES approach, ridgelining, or streamlining.
a. Contour Lines. Emphasizing the main contour lines is a technique used to interpret the terrain of an area. By studying these contour lines, you will get a better understanding of the layout of the terrain and be able to decide on the best route.
(1) Running east to west across the complex landmass is a ridgeline. A ridgeline is a line of high ground, usually with changes in elevation along its top and low ground on all sides. The changes in elevation are the three hilltops and two saddles along the ridgeline. From the top of each hill, there is lower ground in all directions. The saddles have lower ground in two directions and high ground in the opposite two directions. The contour lines of each saddle form half an hourglass shape. Because of the difference in size of the higher ground on the two opposite sides of a saddle, a full hourglass shape of a saddle may not be apparent.
(2) There are four prominent ridges. A ridge is on each end of the ridgeline and two ridges extend south from the ridgeline. All of the ridges have lower ground in three directions and higher ground in one direction. The closed ends of the U's formed by the contour lines point away from higher ground.
(3) To the south lies a valley; the valley slopes downward from east to west. Note that the U of the contour line points to the east, indicating higher ground in that direction and lower ground to the west. Another look at the valley shows high ground to the north and south of the valley.
(4) Just east of the valley is a depression. Looking from the bottom of the depression, there is higher ground in all directions.
(5) There are several spurs extending generally south from the ridgeline. They, like ridges, have lower ground in three directions and higher ground in one direction. Their contour line U's point away from higher ground.
(6) Between the ridges and spurs are draws. They, like valleys, have higher ground in three directions and lower ground in one direction. Their contour line U's and V's point toward higher ground.
(7) Two contour lines on the north side of the center hill are touching or almost touching. They have ticks indicating a vertical or nearly vertical slope or a cliff.
(8) The road cutting through the eastern ridge depicts cuts and fills. The breaks in the contour lines indicate cuts, and the ticks pointing away from the road bed on each side of the road indicate fills.
b. SOSES. A recommended technique for identifying specific terrain features and then locating them on the map is to make use of five of their characteristics known by the mnemonic SOSES. Terrain features can be examined, described, and compared with each other and with corresponding map contour patterns in terms of their shapes, orientations, sizes, elevations, and slopes.
(1) Shape. The general form or outline of the feature at its base.
(2) Orientation. The general trend or direction of a feature from your viewpoint. A feature can be in line, across, or at an angle to your viewpoint.
(3) Size. The length or width of a feature horizontally across its base. For example, one terrain feature might be larger or smaller than another.
(4) Elevation. The height of a terrain feature. This can be described either in absolute or relative terms as compared to the other features in the area. One landform may be higher, lower, deeper, or shallower than another.
(5) Slope. The type (uniform, convex, or concave) and the steepness or angle (steep or gentle) of the sides of a terrain feature.
Through practice, you can learn to identify several individual terrain features in the field and see how they vary in appearance.
NOTE: Further terrain analysis using SOSES can be learned by using the Map Interpretation and Terrain Association Course. It consists of three separate courses of instruction: basic, intermediate, and advanced. Using photographic slides of terrain and other features, basic instruction teaches how to identify basic terrain feature types on the ground and on the map. Intermediate instruction teaches elementary map interpretation and terrain association using real world scenes and map sections of the same terrain. Advanced instruction teaches advanced techniques for map interpretation and terrain association. The primary emphasis is on the concepts of map design guidelines and terrain association skills. Map design guidelines refer to the rules and practices used by cartographers in the compilation and symbolization of military topographic maps. Knowledge of the selection, classification, and symbolization of mapped features greatly enhances the user's ability to interpret map information.
c. Ridgelining. This technique helps you to visualize the overall lay of the ground within the area of interest on the map. Follow these steps:
(1) Identify on the map the crests of the ridgelines in your area of operation by identifying the closeout contours that lie along the hilltop.
(2) Trace over the crests so each ridgeline stands out clearly as one identifiable line.
(3) Go back over each of the major ridgelines and trace over the prominent ridges and spurs that come out of the ridgelines.
The usual colors used for this tracing are red or brown; however, you may use any color at hand. When you have completed the ridgelining process, you will find that the high ground on the map will stand out and that you will be able to see the relationship between the various ridge-lines (Figure 1027).
d. Streamlining. This procedure is similar to that of ridgelining.
(1) Identify all the mapped streams in the area of operations.
(2) Trace over them to make them stand out more prominently.
(3) Then identify other low ground, such as smaller valleys or draws that feed into the major streams, and trace over them.
This brings out the drainage pattern and low ground in the area of operation on the map. The color used for this is usually blue; but again, if blue is not available, use any color at hand so long as the distinction between the ridgelines and the streamlines is clear.