how to read terrain

How to Read Terrain

The following material is excerpted from a publicly available field manual on terrain analysis developed by the U.S. Military.

We share this because the ability to read terrain and maps, and to understand how geography influences operations, is a critical skill for resistance movements. Guerilla resistance movements always find safety in forests and mountains. Know the land.

Terrain Analysis

FM5-33 / July 1990

Terrain analysis, an integral part of the intelligence preparation of the battlefield (IPB), plays a key role in any military operation. During peacetime, terrain analysts build extensive data bases for each potential area of operations. They provide a base for all intelligence operations, tactical decisions, and tactical operations. They also support the planning and execution of most other battlefield functions. Because terrain features continually undergo change on the earth’s surface, data bases must be continuously revised and updated.


This field manual prescribes basic doctrine and is intended to serve as a primary source of the most current available information on terrain analysis procedures for all personnel who plan, supervise, and conduct terrain analysis. The manual discusses the impact of the terrain and the weather on operations.

Part 1: Terrain Evaluation and Verification, Natural Terrain and Surface Configuration

Maneuver commanders must have accurate intelligence on the surface configuration of the terrain. Ravines, embankments, ditches, plowed fields, boulder fields, and rice-field dikes are typical surface configurations that influence military activities.

Elevations, depressions, slope, landform type, and surface roughness are some of the terrain factors that affect movement of troops, equipment, and material.


Landforms are the physical expression of the land surface. The principal groups of landforms are plains or plateaus, hills, and mountains. Within each of these groups are surface features of a smaller size, such as flat lowlands and valleys.

Each type results from the interaction of earth processes in a region with given climate and rock conditions. A complete study of a landform includes determination of its size, shape, arrangement, surface configuration, and relationship to the surrounding area.


Local relief is the difference in elevation between the points in a given area. The elevations or irregularities of a land surface are represented on graphics by contours, hypsometric tints, shading, spot elevations, and hachures.

Slope or Gradient

Slope can be expressed as the slope ratio or gradient, the angle of slope, or the percent of slope. The slope ratio is a fraction in which the vertical distance is the numerator and the horizontal distance is the denominator. The angle of slope in degrees is the angular difference the inclined surface makes with the horizontal plane. The tangent of the slope angle is determined by dividing the vertical distance by the horizontal distance between the highest and lowest elevations of the inclined surface. The actual angle is found by using trigonometric tables. The percent of slope is the number of meters of elevation per 100 meters of horizontal distance.

Slope information that is available to the analyst in degrees or in ratio values may be converted to percent of slope by using a nomogram.

Vegetation Features

Plant cover can affect military tactics, decisions, and operations. Perhaps the most important is concealment. To make reliable evaluations when preparing vegetation overlays, analysts must collect data on the potential effects of vegetation on vehicular and foot movement, cover and concealment, observation, airdrops, and construction materials.


The types of vegetation in an area can give an indication of the climatic conditions, soil, drainage, and water supply. Terrain analysts are interested in trees, scrubs and shrubs, grasses, and crops.

On military maps, any perennial vegetation high enough to conceal troops or thick enough to be a serious obstacle to free passage is classified as woods or brushwood.

Although trees provide good cover and concealment, they can present problems to movement of armor and wheeled vehicles. Woods also slow down the movement of dismounted troops. Individual huge trees are seldom so close together that a tank cannot move between them, but the space between them is often filled by smaller trees or brush. Closely spaced trees are usually fairly small and can be pushed over by a tank; however, the resulting pileup of vegetation may stop the tank. Trees that can stop a wheeled vehicle are usually too closely spaced to bypass.

Trees are classified as either deciduous (broadleaf) or coniferous (evergreen).

With the exception of species growing in tropical areas and a few species existing intemperate climates, most broadleaf trees lose their leaves in the fall and become dormant until the early spring. Needleleaf trees do not normally lose their leaves and exhibit only small seasonal changes.

Scrubs include a variety of trees that have had their growth stunted because of soil or climatic conditions. Shrubs comprise the undergrowth in open forests, but in arid and semiarid areas they are the dominant vegetation. Shrubs normally offer no serious obstacle to movement and provide good concealment from ground observation however, they may restrict fields of fire.

For terrain intelligence purposes, grass more than 1 meter high is considered tall.

Grass often improves the trafficability of soils. Very tall grass may provide concealment for foot troops. Foot movement in savannah grasslands is slow and tiring; vehicular movement is easy; and observation from the air is easy.

Water Features

Safe water, in sufficient amounts, is strategically and tactically important to Army operations. Water that is not properly treated can spread diseases. The control of and access to water is critical for drinking, sanitation, construction, vehicle operation, and other military operations. Military planners are concerned with areas with the highest possibilities for locating usable ground water. They must consider all feasible sources and methods for developing sources when making plans for water supply. Quantity and quality are important considerations. Terrain analysts can use the methods and systems available to locate both surface and subsurface water resources.


Water quantity depends on the climate of the area. Plains, hills, and vegetation are good indicators of water sources.

Large springs are the best sources of water in karstic plains and plateaus. Wells may produce large amounts if they tap underground streams. Shallow wells in low-lying lava plains normally produce large quantities of ground water. In lava uplands, water is more difficult to find, wells are harder to develop, and careful prospecting is necessary to obtain adequate supplies. In wells near the seacoast, excessive withdrawal of freshwater may lower the water table, allowing infiltration of saltwater that ruins the well and the surrounding aquifer.

Springs and wells near the base of volcanic cones may yield fair quantities of water, but elsewhere in volcanic cones the ground water is too far below the surface for drilling to be practicable. Plains and plateaus in arid climates generally yield small, highly mineralized quantities of ground water. In semiarid climates, following a severe drought, an apparently dry streambed frequently may yield considerable amounts of excellent subsurface water. Ground water is abundant in the plains of humid tropical regions, but it is usually polluted. In arctic and subarctic plains, wells and springs fed by ground water above the permafrost are dependable only in summer; some of the sources freeze in winter, and subterranean channels and outlets may shift in location. Wells that penetrate aquifers within or below the permafrost are good sources of perennial supply.

Adequate supplies of ground water are hard to obtain in hills and mountains composed of gneiss, granite, and granite-like rocks. They may contain springs and shallow wells that will yield water in small amounts.

Tree species can also indicate local ground water table presence. Deciduous trees tend to have far-reaching root systems indicating a water table close to the ground surface. Coniferous trees tend to have deep root systems, which depict the ground water table as being farther away from the ground surface. In desert environments, vegetation is scant and specialized to withstand the stress of desert life. Vegetation type is dependent on the water table of that location. Palm trees indicate water within 2 or 3 feet, salt grass indicates water within 6 feet, and cottonwood and willow bees indicate water within 10 to 12 feet. The common sage, greasewood, and cactus do not indicate water levels.


Quality will vary according to the source and the season, the kind and amount of bacteria, and the presence of dissolved matter or sediment. Color, turbidity, odor, taste, mineral content, and contamination determine the quality of water. Brackish water is found in many regions throughout the world but most frequently along sea coasts or as ground water in arid or semiarid climates.


Potable water is free from disease-causing organisms and excessive amounts of mineral and organic matter, toxic chemicals, and radioactivity. Although surface water is ordinarily more contaminated than other sources, it is commonly selected for use in the field because it is more accessible in the quantity required. Ground water is usually less contaminated than surface water and is, therefore, a more desirable water source. However, the use of ground water by combat units is usually limited unless existing wells are available. Rain, melted snow, or melted ice may be used in special instances where neither surface nor ground water is available. Water from these sources must be disinfected before drinking.


Water may be contaminated but not polluted. Streams in inhabited regions are commonly polluted, with the sediment greatest during flood stages. Streams fed by lakes and springs with a uniform flow are usually clear and vary less in quality than do those fed mainly by surface runoff. Generally, the quality of water in large lakes is excellent, with the purity increasing with the distance from the shore. Very shallow lakes and small ponds are usually polluted.


An obstacle is any natural or man-made terrain feature that slows, diverts, or stops the movement of personnel or vehicles. Obstacles are classified as natural, such as escarpments, or man-made, such as built-up areas and cemeteries. They are further categorized as existing-present natural or as man-made terrain features that will limit mobility or as reinforced-existing features that man has enhanced to use as obstacles, such as gentle slopes reinforced by tank ditches, pikes, or revetments that limit mobility of maneuver units.

For classification purposes, obstacles must beat least 1.5 meters high and 250 meters long and have a slope greater than 45 percent (that which military vehicles are unable to travel). Obstacles that will be delineated should be in areas where they are of primary importance for the diversion of crosscountry movement.

Obstacles include escarpments, embankments, road cuts and fills, depressions, fences, walls, hedgerows, and moats.

Urban Areas

Urban-area intelligence is important in planning tactical and strategical operations, targeting for nuclear or air attack, and planning logistical support for operations. Knowledge of characteristics in urban areas may also be important in civil affairs, intelligence, and counterintelligence operations. Although information is frequently accessible, the amount of detail required necessitates a substantial collection effort.

The first aspect of urban intelligence includes geographic location, relative economic and political importance of urban areas in the national structure, and physical dimensions such as street shapes. The six street patterns are rectangular, radial, concentric, contour conforming, medieval irregular, and planned irregular (in the new residential suburbs of some countries).

The second aspect includes physical composition, vulnerability, accessibility, productive capacity, and military resources of individual urban areas. Urban areas are significant as military objectives or targets and as bases of operations. They may be one or a combination of power centers (political, economic, military); industrial production centers; service centers; transportation centers; population centers; service centers (distribution points for fuels, power, water, raw materials, food, manufactured goods); or cultural and scientific centers (seats of thought and learning, and focal points of modem technological developments).

Buildings can provide numerous concealed positions for the infantry. Armored vehicles can find isolated positions under archways or inside small industrial or commercial structures. Thick masonry, stone, or brick walls offer excellent protection from direct fire, and ceilings for individual fire. Cover and concealment can also be provided by the percentage of roof coverage. For detailed information, see FM 90-10.


Analysts preparing terrain studies must carefully evaluate all transportation facilities to determine their effect on proposed operations. Analysts may recommend destroying certain facilities or retaining them for future use. The entire transportation network must be considered in planning large-scale operations. An area with a dense transportation network, for example, is favorable for major offensives. Networks that are criss-crossed by canals and railroads and possess few roads will limit the use of wheeled vehicles and the maneuver of armor and motorized infantry.

The transportation facilities of an area consist of all highways, railways, and waterways over which troops or supplies can be moved. The importance of each area depends on the nature of the military operation involved. An army’s ability to carry out its mission depends greatly on its transportation capabilities and facilities.


Military interest in highway intelligence of a given area or country covers all physical characteristics of the existing road, track, and trail system. All associated structures and facilities necessary for movement and for protection of the routes, such as bridges, ferries, tunnels, and fords, are integral parts of the highway system.

The severe abuse given to roads by large volumes of heavy traffic, important bridges, intersections, and narrow defiles makes them primary targets for enemy bombardment.


Railways are a highly desirable adjunct to extended military operations. Their capabilities are of primary concern and are the subject of continuing studies by personnel at the highest levels.

Railroads include all fixed property belonging to a line, such as land, permanent way, and facilities necessary for the movement of traffic and protection of the permanent way. They include bridges, tunnels, snowsheds, galleries, ferries, and other structures.


Structures and crossings on highways or railways include bridges, culverts, tunnels, galleries, ferries, and fords. For the purpose of terrain intelligence, they also include cableways, tramways, and other features that may reduce or interrupt the traffic flow on a transportation route. Bridges and culverts are the structures most frequently encountered; however, any feature that may present a potential obstacle is significant in a military operation.

Any type of structure or crossing on a transportation route is an important portion of the route regardless of the mode of transportation. Maps, charts, photographs, and other sources contain valuable information that analysts should exploit.

Highway and railway bridges and tunnels are vulnerable points on a line of communications. Information about prevention, destruction, or repair of a bridge may be the key to an effective defense or the successful penetration of an enemy area. A bridge seized intact has great value in offensive operations, since even a small bridge eases troop movement over a river or stream.


Pipelines that carry petroleum and natural gas represent an important mode of transportation. White rail, water, and road transport are used extensively for transporting fluids and gases, the overland movement of petroleum and refined products is performed most economically and expeditiously by pipeline. Crude-oil pipelines are used only to transport crude oil, while many refried-product pipelines carry more than one product. These products are sent through the pipelines in tenders, or batches, to keep the amount of mixing to a minimum. Because of their most vital link in an industrialized country’s energy supply system, coal and ore are also carried in pipelines as slurry.

Terminal Facilities

Refinery terminals consist of numerous tanks for the separate storage of crude oil and refined products. Facility size and type depends on whether the refinery is located near the source of supply or consuming center, Refined-product dispensing terminals contain a variety of products for final distribution. –

Natural gas is generally stored in bulk, below the ground, and under high-pressure, Large underground gas storage pools, usually caves or quarries near consuming centers, are often used to store gas for seasonal or emergency needs. Above ground, natural gas is stored mostly under pressure in spherical tanks, but large telescoping tanks are sometimes used for low-pressure storage. Natural-gas receiving terminals are located at the producing field and contain facilities for conditioning the gas for pipeline transmission. Natural-gas dispensing terminals are located at consuming centers and include dispatching and metering facilities and sufficient storage facilities to meet peak demands.

Storage tanks, found in varying numbers at all petroleum installations, are easily recognized. Volatile products such as gasoline and kerosene are generally stored in floating roof tanks. These tanks have roofs that float on the liquid to reduce space in which vapor might form. Nonvolatile products such as fuel oils and crude oil are stored in fixed-roof tanks. Petroleum gases are generally liquefied and stored under pressure in spherical tanks or in horizontal cylindrical tanks. The number and variety of tanks in a storage installation indicate the quantity and types of product stored. Areas of great extent and capacity are called tank farms.

Ports and Harbors

Information about ports, naval bases, and shipyard facilities is essential for estimating capacities, vulnerability, and other items of military significance.

Ports are settlements with installations for handling waterborne shipping. Principal port facilities are berthing space, storage space, cargo-handling equipment, cargo transshipment facilities, and vessel-servicing facilities. Ports are classified on an area-wide rather than a worldwide basis, and a principal port in a small maritime nation may be equivalent to a much lesser port in the more extensive port system of another country. In wartime, principal and secondary ports and bases are prime targets for destruction, and the relative importance of minor ports increases.

Further Reading and Study

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