text: Chapter 7
  terrain masking, and smoke. Line of sight is an unobstructed path from a Soldier weapon, weapon sight,
  electronic sending and receiving antennas, or reconnaissance equipment from one point to another.
  7-25. Observation and field of fire require special consideration in urban environments such as
  observation and weapons effects. Urban situations create a lot of dead space. However, high structures
  generally offer excellent observation. Line of sight distances may decrease in urban settings.
  Avenue of Approach
  7-26. This is an air or ground route of an attacking force (friendly or threat) leading to its objective or
  key terrain. Avenues of approach normally show the size of unit that can use them.
  Key Terrain
  7-27. This refers to any place whose seizure, retention, or control affords a marked advantage to either
  combatant. In an urban environment, key terrain can include tall structures, choke points, intersections,
  bridges, industrial complexes, or other facilities, for example. High ground can serve as key terrain,
  because it dominates an area with good observation and fields of fire. In an open or arid environment, a
  draw or wadi could serve as key terrain.
  7-28. Decisive terrain is key terrain that has an extraordinary impact on the mission. The successful
  accomplishment of the mission depends on seizing, retaining, or denying decisive terrain to the threat. Note
  that key terrain is not necessarily decisive. The commander designates decisive terrain to show his staff and
  subordinate commanders how important that terrain is to his concept of the operation.
  7-29. Other services emphasize the importance of the population, and include groups of people such as
  ethnic groups, the media, or political parties as terrain, and in some cases key terrain. However, the US
  Army does not consider people to be terrain.
  Obstacles
  7-30. An obstacle is any obstruction designed or employed to disrupt, fix, turn, or block the movement
  of a threat, and to impose additional losses in personnel, time, and equipment on the threat. Obstacles can
  be natural, manmade, or a combination of both. Some examples are--
  • Buildings.
  • Mountains.
  • Steep slopes.
  • Dense forests.
  • Rivers.
  • Lakes.
  • Urban areas.
  • Minefields.
  • Certain religious and cultural sites.
  • Wire obstacles such as concertina wire, barbed wire.
  7-31. Obstacles could affect certain types of movement differently. As an example, obstacles such as
  rivers, lakes, swamps, densely forested areas, road craters, rubble in streets, or dense populations in urban
  areas may have a greater effect on mounted movement than on dismounted movement. Mine fields,
  concertina wire, or steep slopes may have a greater effect against dismounted movement. Obstacles that
  can affect air mobility include terrain features that are higher than an aircraft’s service ceiling, that restrict
  nap-of-the-earth flight, or that force the aircraft to use a particular flight profile. Examples include tall
  buildings (skyscrapers), cell phone towers, phone and power lines, rapidly rising terrain features,
  mountains, smoke, and other obscurants. High mountains can impact rotary- and fixed-wing aircraft lift
  capabilities.