Unit 6: Contouring Topics covered Basic definitions Characterstics of coutour Unit 10: Contouring

Plan or map Only shows the horizontal position of points Unit 10: Contouring

Topographic map Source: www.topozone.com Unit 10: Contouring

Different methods of showing elevations Source: www.topozone.com Unit 10: Contouring Source: www.howardweb.com

10.1 Basic definitions- Contour The most common method of representing the topography of an area is to use contour lines Contours A contour line is an imaginary line that connects points of equal elevation If you walk along a contour line you neither gain or lose elevation.   they allow us to show the shape of the land surface (topography) on a map Source: www.raider.muc.edu Unit 10: Contouring

10.1 Basic definitions Source: www.raider.muc.edu Unit 10: Contouring

10.1 Basic definitions Source: www.raider.muc.edu Unit 10: Contouring

10.1 Basic definitions Source: www.raider.muc.edu Unit 10: Contouring

10.1 Basic definitions Imagine a hill that has its top sliced off with a really big knife Unit 10: Contouring

10.2 Contour interval Contour interval Contour lines can be drawn for any elevation, but to simplify things only lines for certain elevations are drawn on a topographic map These elevations are chosen to be evenly spaced vertically This vertical spacing is referred to as the contour interval The vertical distance between two consecutive contours is Kept constant for a contour plan Unit 10: Contouring

10.2 Contour interval Choice of Contour interval depends upon: The nature of ground For flat ground, small interval is chosen For undulated, broken ground greater (relative term) interval is chosen The scale of the map Inversely proportional to the scale of map For general topographical work, following rules can be followed The purpose and extent of survey For detailed design work or accurate earthwork calculation, small interval is chosen For large extent work such as drainage area, lines of communication, large interval is chosen Time and expense of field and office work Unit 10: Contouring

Horizontal equivalent The horizontal distance between two points on two consecutive contours Depends up on the steepness of the ground Large horizontal equivalent Small horizontal equivalent Unit 10: Contouring

Index contour Index contour It is not possible to label the elevation of each contour line To make the map easier to read every fifth contour line is marked with elevation. This contour line is an index contour Index contours are shown by darker brown lines on the map Source: www.raider.muc.edu Unit 10: Contouring

10.2 Characteristics of contour Closely spaced contours indicate steep slopes Widely spaced contours indicate moderate slopes Source: www.topozone.com A contour line must close itself, though not necessarily within the limits of the map Unit 10: Contouring

10.2 Characteristics of contour Depression and hill look the same; note the contour value to distinguish the terrain Depression without outlet Hill Source: Surveying Vol I by B.C. Punmia Unit 10: Contouring

10.2 Characteristics of contour Contour lines tend to parallel each other on uniform slopes Contour lines are parallel, straight and equally spaced in case of inclined plane surface Source: Surveying Vol I by B.C. Punmia A contour passing through any point is perpendicular to the line of steepest slope at that point Source: Surveying Vol I by B.C. Punmia Unit 10: Contouring

10.2 Characteristics of contour Contour line do not cross except in the case of overhanging cliff or a cave. Source: Surveying Vol I by B.C. Punmia Unit 10: Contouring

10.2 Characteristics of contour Contour lines of different elevation can unite to form one line only in the case of a vertical cliff. Source: www.raider.muc.edu Unit 10: Contouring

10.2 Characteristics of contour Contour lines cross a watershed or ridge and valley line at right angle Watershed or ridge line form curves of U-shape round it with the concave side of the curve towards the higher ground Valley line form sharp curves of V-shape across it with convex side of the curve towards the higher ground Source: Surveying Principle and Applications by Barry F. Kavanagh & S.J. Glenn Bird Unit 10: Contouring

10.2 Characteristics of contour Source: www.topozone.com Unit 10: Contouring

10.2 Characteristics of contour Source: www.topozone.com Unit 10: Contouring

Thank you for your attention! Any questions? Querries? Unit 10: Contouring