What is Topography?
The topography is the science and study of a land surface. This includes hills, mountains, valleys, rivers. Topography not only includes natural features, but also includes artificial features such as roads, bridges, and buildings. In short, Topography is a representation of the existing features of a piece of land. The topography is very closely associated with Surveying. Developments in GIS (Geographic Information System) allows the creation of complex topographical maps.
Topographic Surveys primarily include elevation contours or points. These eventually produce a three-dimensional surface. The points are measured in terms of horizontal coordinates and the elevation (X, y, and Z coordinates). These points are recorded as a series. When these are connected, they produce contour lines.
Applications of Topography
Topographical Surveys are used for a wide range of purposes. Some of these include:
- Architects use the Topographical surveys to place buildings appropriately on a site to take advantage of views, minimize leveling costs and relate to existing facilities and buildings
- Urban Designers use the Topographical Surveys to plan an area or for Urban Renewal Projects. You need to plan in a manner that utilizes natural slopes to manage water-run off
- Infrastructure Planners use Topographical Surveys to plan out Roads, Bridges, and flyovers
Topographical Survey Techniques
Topographical Surveys are created using a variety of methods that depend on the area to be surveyed, the level of detail that is required, and the end-use of this Survey. Broadly, these are two categories, Direct/ Manual Surveys, and aerial surveys. Surveyors either provide a tabulated data or a Contour Plan typically in AutoCAD DWG format.
Manual Surveys are done using instruments such as Theodolite. Theodolite measures, distance, angle. Theodolite can measure angles in both horizontal and vertical planes.
GIS (Geographic Information Systems)
GIS technology and process integrates digital data obtained from 3D Photographic Maps, that are converted to CAD format.
LIDAR (Light Detection and Ranging)
Lidar can produce extremely accurate terrain Models, even in difficult situations such as dense foliage. Lidar is like Radar, in terms of measurement using delay in wave signals.
Photogrammetry uses stereographic photographs to measure point coordinates and their elevations.
Contours or Contour Lines
Contours or Contour lines are imaginary lines that connect points representing a level or elevation in relation to a base point or mean sea level. Contours that are close to each other, represent steeper slopes as compared to areas where contour lines are far apart. This is called Gradient. Contour Interval, as we have seen earlier, each contour line represents a level. Contour Interval is the level difference between two contour lines.
Topography Survey Units and Scale
Topographic Surveys that we get are usually in DWG format and can be opened and edited in AutoCAD or other CAD software that can read DWG files. You need to be aware that these surveys are often drawn to scale mentioned in the drawing, unlike to full scale, in which we make our typical drawings. Secondly, ensure that the units are correctly set. There have been situations, where even though, units are set to metric, but the distances and measurements are in imperial units. Learn more about Creating Toposurface from imported CAD