Dashed Line

A dashed line is a line consisting of a series of dashes or short lines separated by spaces.  It is often used in maps to indicate boundaries or other features that are not well defined. In topographical maps, dashed lines may represent different types of terrain, such as ridges, valleys, or cliffs.  They may also be used to show paths, trails, or roads that are not paved or easily accessible.  Dashed lines are an important tool for map readers to interpret the landscape and understand the topography.

Datum

A datum is a reference point or surface used to measure distances, elevations, or depths.  It is a fixed point from which all other measurements are made.  In topography and geodetic surveys, a datum is typically a well-defined point or surface, such as the mean sea level or a benchmark.  Datum is an essential tool for measuring changes in elevation or depth over time, as well as for determining the location of underground features such as water tables or oil reserves. Datum can be established using various methods, including satellite imagery, GPS, or traditional surveying techniques.

Datum Level

Datum level is a reference point used in surveying and topography to establish elevations and depths.  It is a fixed point or surface from which all other measurements are made. In geodetic surveys, the datum level is typically the mean sea level, while in land surveys it can be a benchmark or a known elevation.  Datum level is an essential tool for engineers, architects, and construction workers to ensure that structures are built to a consistent height and elevation. It is also important for floodplain management, as it helps to determine the extent of potential flooding.

Dead Reckoning

Dead reckoning is a method of navigation used in topography and marine navigation to determine one’s position based on known speed and direction of travel. It involves estimating the distance traveled and the direction taken, without relying on external landmarks or references. Dead reckoning can be a useful tool for navigating through open water or difficult terrain where landmarks are scarce or not easily visible.  However, it is prone to error and requires accurate measurements of speed and direction to be effective.  Dead reckoning can be supplemented by other methods of navigation, such as GPS or celestial navigation, to increase accuracy and ensure safety.

Declination Diagram

A declination diagram is a graphical representation of the angle between true north and magnetic north, known as magnetic declination.  It is an essential tool for navigation and orientation in topography, as it helps to adjust for the difference between true north and magnetic north.  The declination diagram shows the difference between the two norths in degrees, and it is typically depicted as a series of lines on a map or chart.  By using a declination diagram, navigators can accurately determine their heading and ensure that they are traveling in the right direction.

Declination

Declination is the angle between true north and magnetic north, and it is an important factor in topographical navigation.  It varies depending on location and time, and it is affected by changes in the Earth’s magnetic field.  Declination is typically measured in degrees, and it can be positive or negative depending on the direction of magnetic north relative to true north.  In order to navigate accurately, it is necessary to adjust for declination by using a declination diagram or a magnetic compass. Failure to account for declination can result in incorrect navigation and potentially dangerous situations.

Degree

Degree is a unit of measurement used in topography and many other fields to express angles and arcs.  It is defined as 1/360th of a full rotation, or circle. Degrees are commonly used to measure angles of elevation or depression, as well as horizontal angles.  In topography, degrees are used to measure the slope of hills and mountains, and to express the direction of compass bearings.  Degrees can be further divided into minutes and seconds, which allow for greater precision in measurement.  A degree is an essential tool for map reading, navigation, and surveying, and it is a fundamental concept in geometry and trigonometry.

Delta

Delta is a landform that is formed at the mouth of a river, where it meets a larger body of water such as an ocean or a lake. It is characterized by a fan-shaped accumulation of sediment, typically consisting of sand, silt, and clay.  Deltas are an important part of topographical landscapes, as they provide fertile soil for agriculture and support a variety of aquatic and terrestrial ecosystems.  They can also be important for shipping and transportation, as they often provide natural harbors and ports.  Deltas are constantly changing and evolving due to changes in water flow and sediment deposition, and they can be influenced by human activities such as damming and land use change.

Deposition

Deposition is the process by which sediment, soil, or other materials are laid down or accumulated in a specific location.  It is a natural process that occurs in many topographical environments, such as rivers, lakes, and oceans.  Deposition can be caused by a variety of factors, including erosion, weathering, and transport by wind or water.  It is an important process for creating and shaping landforms, such as beaches, dunes, and river deltas. Deposition can also have practical applications, such as in the formation of mineral deposits or in the creation of artificial islands.

Depression

A depression is a topographical feature that is characterized by a sunken or lowered area of land.  It is typically surrounded by higher ground and can be caused by a variety of geological processes, including erosion, weathering, and subsidence.  Depressions can range in size from small pits to large basins, and they can occur in a variety of environments, such as deserts, wetlands, and mountainous regions.  They can also be formed by human activities, such as mining or excavation.  Depressions can have important ecological functions, such as providing habitat for wildlife, as well as practical uses, such as collecting and storing water.

Depth Curve

A depth curve is a graphical representation of the depth of a body of water at various points.  It is an important tool for navigation and marine exploration, as it provides detailed information about underwater terrain.  Depth curves are typically depicted on nautical charts, and they use a series of contour lines to show changes in depth.  The lines are spaced at regular intervals and are labeled with the corresponding depth.  By using a depth curve, sailors and navigators can accurately determine their position and avoid potential hazards such as underwater shoals or reefs.

Depth Interval

Depth interval is the distance between contour lines on a topographical map that represents changes in depth or elevation.  It is an important factor in map reading and navigation, as it provides a measure of the slope and steepness of the terrain.  The depth interval is typically chosen based on the scale of the map and the level of detail required.  A larger depth interval is used for smaller-scale maps, while a smaller depth interval is used for larger-scale maps.  By understanding the depth interval, map readers can accurately interpret the landscape and plan routes that take into account changes in elevation and depth.

Depth Sounder

A depth sounder is a device used to measure the depth of water beneath a boat or ship.  It works by emitting a sound wave that travels through the water and bounces off the seabed or other underwater features, such as rocks or debris.  The time it takes for the sound wave to return to the depth sounder is used to calculate the depth of the water.  Depth sounders are an essential tool for navigation, as they provide crucial information about underwater terrain that can be used to avoid hazards such as shoals, reefs, or other obstructions.

Depth Soundings

Depth soundings are measurements taken using a depth sounder to determine the depth of water beneath a boat or ship.  They are typically recorded on nautical charts and used for navigation and marine exploration.  Depth soundings can vary depending on the scale of the chart and the level of detail required.  In shallow waters, they may be taken every few meters, while in deeper waters, they may be taken every few hundred meters.  By understanding the depth soundings, sailors and navigators can plan safe and efficient routes that take into account changes in water depth.

Desert

A desert is a topographical region characterized by arid or dry conditions and minimal vegetation cover.  Deserts can be found on every continent and are typically located in areas that receive less than 10 inches of precipitation per year.  They are often characterized by extreme temperature fluctuations, with hot days and cold nights.  Deserts can be home to a variety of plants and animals that have adapted to the harsh conditions, such as cacti, succulents, and desert rodents.  They can also be important cultural and historical sites, such as ancient trade routes or sacred sites for indigenous communities.

Desert Pavement

Desert pavement is a topographical feature found in arid regions that is characterized by a surface layer of closely packed stones or gravel.  It is created over time through a process of erosion, where wind and water remove finer materials and leave behind larger rocks and stones.  Desert pavement can vary in thickness and composition, and it can be an important factor in controlling erosion and water runoff in desert environments.  It can also have cultural and historical significance, as it has been used by indigenous communities for thousands of years for activities such as tool-making, hunting, and gathering.

Detached Contour

A detached contour is a contour line on a topographical map that does not connect to adjacent contour lines of the same elevation.  Detached contours typically indicate a change in elevation that is abrupt or steep, such as a cliff or a steep slope.  They are represented by short, straight lines that connect the detached contour to the surrounding contour lines.  Detached contours can be useful for identifying potential hazards or obstacles in the terrain, such as areas that may be difficult to traverse on foot or dangerous to approach.

Deviation Angle

A deviation angle is the angle between true north and magnetic north.  This angle varies depending on the location of the observer and the strength and direction of the Earth’s magnetic field.  Deviation angles are important for navigation and orienteering, as they can affect the accuracy of a compass reading.  To correct for deviation, navigators may use a deviation card, which lists the deviation angles for different headings and compass directions. By applying the appropriate correction, navigators can ensure that their compass readings are accurate and reliable.

Diagonal Marks

Diagonal marks are a symbol used on topographical maps to indicate steep slopes or cliffs.  They are typically shown as a series of diagonal lines crossing the contour lines at a 45-degree angle.  The density and spacing of the diagonal marks can indicate the degree of slope or the severity of the cliff.  Diagonal marks are important for identifying potential hazards in the terrain, such as areas that may be difficult to traverse on foot or dangerous to approach.

Differential Leveling

Differential leveling is a surveying technique used to determine the difference in elevation between two points on the Earth’s surface.  It works by measuring the vertical distance between two points using a surveying rod and a level instrument.  Differential leveling can be used to create detailed maps of the terrain, determine the height of buildings or other structures, or plan construction projects.  It is a precise and accurate method of measurement, and it is commonly used in engineering, construction, and land management.

Digital Elevation Model (DEM)

A digital elevation model (DEM) is a digital representation of the Earth’s surface, typically created using satellite or aerial data.  A DEM contains information about the elevation and slope of the terrain, and it can be used to create detailed topographical maps, calculate water runoff, or plan construction projects.  DEMs are often used in geographic information systems (GIS) to model and analyze the landscape.  They can be displayed as 3D models or as 2D contour maps, and they are a valuable tool for scientists, engineers, and planners.

Dike

A dike is a type of embankment or barrier used to control or redirect the flow of water.  Dikes are typically made of earth, rock, or concrete and are used to prevent flooding, reclaim land, or create reservoirs.  Dikes can be found along rivers, coastlines, and other areas where flooding is a risk.  They are often used in conjunction with other water management techniques, such as levees, dams, or canals.

Dip

In geology, the term “dip” refers to the angle of a rock layer or fault relative to the horizontal plane.  The dip is measured perpendicular to the strike, which is the direction in which the rock layer or fault is oriented.  The dip can be used to determine the structure and orientation of the rock layers in a particular area, which can be important for understanding the geological history of the region.  Dips are commonly measured using a specialized tool called a clinometer.

Direction

In topography, direction refers to the orientation of a particular feature or landmark relative to other features in the landscape.  Directions can be expressed using compass bearings or cardinal directions, such as north, south, east, or west.  Understanding the direction of various features in the landscape can be important for navigation, orienteering, and map reading.  It can also be important for understanding the geological history of a particular region, as the orientation of rock formations or fault lines can provide clues about the forces that shaped the landscape over time.

Directivity

Directivity refers to the directional pattern of a sound or electromagnetic wave.  In topography, directivity can be important for understanding how sound or electromagnetic waves propagate through the landscape.  For example, the directivity of a sound wave can affect how it is reflected or absorbed by different features in the landscape, such as mountains, valleys, or forests.  Understanding the directivity of different types of waves can be important for a variety of applications, including communication, remote sensing, and seismic studies.

Discharge

Discharge refers to the volume of water that flows through a river or stream over a specific period of time.  Discharge can be measured in cubic meters per second or other units of volume per unit of time.  Understanding the discharge of a river or stream can be important for a variety of applications, including water management, hydroelectric power generation, and ecological studies.  Discharge can be affected by a variety of factors, such as precipitation, evaporation, and the topography of the surrounding landscape.

Discontinuity

In geology, a discontinuity is a break or separation in a rock formation. Discontinuities can be caused by a variety of factors, including faulting, erosion, or the intrusion of a different type of rock. D iscontinuities can be important for understanding the structural and geological history of a region, as they can provide clues about the forces that shaped the landscape over time.  Discontinuities can also affect the stability of rock formations and can be important for engineering and construction projects.

Displacement

Displacement refers to the movement or shifting of a geological feature, such as a rock formation or fault line, due to tectonic forces or other geological processes.  Displacement can be measured in terms of the distance and direction of the movement.  Understanding the displacement of different features in the landscape can be important for understanding the geological history of a region and for predicting seismic activity. Displacement can also be important for engineering and construction projects, as it can affect the stability of the ground and the safety of structures built on top of it.

Distance

Distance refers to the measurement of space between two points.  In topography, distance can be important for understanding the layout of the landscape and for navigation.  Distance can be measured in a variety of units, such as meters, kilometers, or miles.  Understanding the distance between two points can be important for a variety of applications, including surveying, mapping, and hiking or driving directions.

District

A district is a defined area or region, often with distinct boundaries and administrative or political functions.  In topography, districts can be important for understanding the organization of a region and for tracking changes over time. D istricts can be defined based on a variety of factors, such as geography, population, or land use.  Understanding the different districts within a region can be important for a variety of applications, including urban planning, resource management, and political analysis.

Ditch

A ditch is a narrow channel dug into the ground, often for the purpose of drainage or irrigation.  In topography, ditches can be important for understanding the hydrology and water management practices of a region.  Ditches can be dug by humans or can occur naturally, and can be made from a variety of materials, such as dirt, stone, or concrete.  Understanding the location and function of ditches within a landscape can be important for a variety of applications, including water management, agriculture, and construction.

Divide

A divide is a geological feature that separates the drainage basins of different rivers or streams. In topography, divides can be important for understanding the flow of water within a region and for predicting the location and behavior of rivers and streams.  Divides can be formed by a variety of factors, such as mountain ranges, ridges, or plateaus.  Understanding the location and structure of divides can be important for a variety of applications, including water management, ecological studies, and transportation planning.

Doline

A doline is a type of landform that occurs when limestone or other soluble rock dissolves, causing the land surface above to sink and form a depression. In topography, dolines can be important for understanding the geology and hydrology of a region.  Dolines can range in size from small depressions to large sinkholes, and can be found in many parts of the world.  Understanding the location and formation of dolines can be important for a variety of applications, including land management, environmental conservation, and geological research.

Dome

A dome is a type of landform that occurs when rocks are uplifted and form a circular or elliptical structure, with the oldest rocks in the center and younger rocks on the outer edges.  In topography, domes can be important for understanding the geology and structure of a region.  Domes can range in size from small hills to large mountain ranges, and can be found in many parts of the world.  Understanding the location and formation of domes can be important for a variety of applications, including geological research, resource management, and urban planning.

Dominant Feature

A dominant feature is a prominent landform or feature that stands out in a landscape and can be easily identified from a distance.  In topography, dominant features can be important for navigation and orientation, as well as for understanding the layout and organization of a region.  Dominant features can include mountains, hills, valleys, rivers, or other prominent natural or human-made features.  Understanding the location and significance of dominant features can be important for a variety of applications, including tourism, land management, and military strategy.

Drainage Basin

A drainage basin, also known as a catchment area or watershed, is an area of land that collects and drains water to a common outlet, such as a river, lake, or ocean. In topography, drainage basins can be important for understanding the flow of water within a region and for predicting the location and behavior of rivers and streams. Drainage basins can range in size from small watersheds to large river basins, and can be found in many parts of the world. Understanding the location and boundaries of drainage basins can be important for a variety of applications, including water management, ecological studies, and transportation planning.

Drainage Divide

A drainage divide is a high point or ridge of land that separates two adjacent drainage basins.  It is the boundary between the areas where surface water drains to different bodies of water, such as rivers, lakes, or oceans.  In topography, drainage divides can be important for understanding the flow of water within a region and for predicting the location and behavior of rivers and streams.  Drainage divides can be natural or man-made, and can be found in many parts of the world.  Understanding the location and characteristics of drainage divides can be important for a variety of applications, including water management, land-use planning, and ecological studies.

Draw

A draw is a small, steep-sided valley or gully that is typically dry and formed by the erosion of soil and rock by water. In topography, draws can be important for understanding the hydrology and erosion patterns of a region.  Draws can be found in many different environments, from desert regions to mountainous areas, and can vary in size from small gullies to large valleys.  Understanding the location and formation of draws can be important for a variety of applications, including land management, agricultural practices, and geological research.

Drumlin

A drumlin is a long, smoothly rounded hill that is formed by glacial deposition during the last Ice Age.  In topography, drumlins can be important for understanding the glacial history and geology of a region.  Drumlins can range in size from a few meters to several kilometers in length, and are typically oriented in the direction of ice flow.  Understanding the location and formation of drumlins can be important for a variety of applications, including geological research, resource management, and urban planning.

Dune

A dune is a hill or ridge of sand that is formed by wind or water erosion and deposition.  In topography, dunes can be important for understanding the erosion and sediment transport patterns of a region.  Dunes can be found in many different environments, from deserts to coastal areas, and can vary in size from small ripples to large sand hills.  Understanding the location and formation of dunes can be important for a variety of applications, including land management, ecological studies, and tourism.

Dynamic Map

A dynamic map is a digital map that is interactive and allows users to customize and interact with the displayed information.  In topography, dynamic maps can be im portant for visualizing and analyzing complex spatial data.  Dynamic maps can display a wide range of information, including elevation, land cover, and transportation networks.  They can also allow users to interact with the data by zooming in and out, changing the display settings, and accessing additional information.  Understanding the use and design of dynamic maps can be important for a variety of applications, including urban planning, resource management, and environmental conservation.