Topography is a broad term used to describe the detailed study of the earth’s surface. This includes changes in the surface such as mountains and valleys as well as features such as rivers and roads. It can also include the surface of other planets, the moon, asteroids and meteors. Topography is closely linked to the practice of surveying, which is the practice of determining and recording the position of points in relation to one another.
The word topography itself is derived from the greek “topo,” meaning place, and “graphia,” meaning to write, or to record. Some of the first known topographic surveys were conducted by the British military in the late eighteenth century. In the United States, the earliest detailed surveys were made during the War of 1812 by the “Topographical Bureau of the Army.” Throughout the twentieth century topographical mapping became more complex and precise with the invention of instruments such as theodolites and automatic levels. Most recently, developments in the digital world such as GIS (geographic information system) have allowed us to create increasingly complex topographical maps.
Modern-day topography is generally concerned with the measurement and recording of elevation contours, producing a three-dimensional representation of the earth’s surface. A series of points are chosen and measured in terms of their horizontal coordinates, such as latitude and longitude, and their vertical position, in terms of altitude. When recorded in a series, these points produce contour lines which show gradual changes in the terrain.
The most widely used form of measurement is known as Direct Survey. This is the process of manually measuring distances and angles using leveling instruments such as theodolites. Direct surveying provides the basic data for all topographic mapping, including digital imaging systems. This information can be used in conjunction with other systems such as aerial photography or satellite imagery to provide a complete picture of the land in question.
Sonar mapping is the primary technique used to map the ocean floor. A pulse of sound is sent through the water from an underwater speaker, and is reflected back again by objects in the water, such as the ocean bottom, coral beds, or a submarine. Microphones measure the reflected sound waves. The time that the echo takes to return is proportional to the distance of the reflecting object. This data allows changes in the underwater terrain and other objects likes shipwrecks to be mapped.
A topographic study can be used for a variety of applications such as military planning and geological exploration. Detailed information about terrain and surface features is also essential for the planning and construction of any major civil engineering or construction projects. More recently, large scale surveys such as Google Maps have been produced using satellite technology, providing the first complete, widely available surveys of the earth.
Digital Mapping Systems
There are a variety of digital systems which utilize the basic data collected from topographic surveying to produce maps:
GIS uses computer software to create highly detailed maps with distinct layers displaying almost any type of element, such as roads, bridges, buildings, rivers, political boundaries, soil types,
3-D rendering uses satellite or aerial images to produce a three-dimensional model using computer software.
Aerial photography and photogrammetry combine photos from different angles and use the process of triangulation to calculate the location of elements.