Review of Related Literature

Topography

Topography refers to the configuration, shape and roughness, of the ground. Topographic

surveys determine the locations of natural and artificial features and elevations used in map making.

Topographic maps show the spatial characteristics of the Earth’s surface along with natural and

manmade structures present. They are commonly used during the planning stages of a construction

project. Topographic maps help in designing the layout and location of buildings, roads, dams, and other

structures in such a way that will ensure stability to said structures.

Relief Representation

Topographic maps are distinguished from other kinds of maps by its usage of different symbols

and methods for describing relief. Some commonly used symbols and methods are listed below:

Contour Lines – a line that goes through points of equal elevation the map.

Spot Heights/Elevations – indicates the elevation of specific points. Spot heights are

usually used on important locations/features.

Hachures – multiple short parallel lines that produces an effect similar to shading.

Subaqueous Contours – similar to contour lines but are used to portray underwater

ground. Drawn in blue lines to avoid confusion with contour lines.

Contours

Among the symbols commonly used in topographic maps mentioned above contours are most

often used to show relief because they can give an accurate quantitative representation of the ground’s

terrain. The vertical distance between two contour lines in a map is referred to as the contour interval. It

is dependent on the purpose and scale of the map. A terrain with small to moderate elevation

differences would benefit more from a small contour interval. Mountainous or rugged areas with large

elevation differences on the other hand would require a larger contour interval as to not crowd the map

with too much contour lines. In regions where both flat and mountainous areas are present,

supplementary contours, a kind of contour line, are used alongside regular contour lines to better depict

the area relief. Supplementary contours are usually drawn using dashed lines. In maps, only elevations

that can only be divided evenly by the contour interval are drawn as contour lines.

Contour lines have a specific set of characteristics that they follow. These characteristics should

be used as guidelines when drawing contours.

1. Contour lines must close on themselves, either on or off a map.

2. Closely spaced contour signifies steep slope while widely spaced contours indicate a gentle

slopes.

3. On slopes that are of uniform elevation, contour lines are evenly spaced.

4. Contours cannot intersect/cross one another on the map, except on overhanging cliffs.

5. The slope between adjacent contour lines is assumed to be uniform.

6. Irregular contour symbolizes rough terrain. Smooth lines represent uniform terrain.

7. Contours that form a circle that increase in elevation represents hills/mountains.

8. A depression contour is usually represented with closed loops around lower ground, hachures

towards the bottom, and a spot elevation at the lowest point.

9. A contour cannot branch into two contours of the same elevation.

10. Contour lines crossing a stream point upstream and form V’s; they point

down the ridge and form U’s when crossing a ridge crest.

11. A single contour of a given elevation cannot exist between two equal height contours of higher

or lower elevation.

Following these guidelines will help in preventing mistakes in drawing contours and will make it

easier

to visualize them when looking at an area.

Locating Topographic Details

Features to be included in a topographic map can range from point features such as trees or

lines for roads to complicated land formations. Detailing is the process of locating points that are to be

included in the map. Locating contours/features can be accomplished by any one of the following

procedures listed below:

1. Radiation by Total Station

- The total station is set up in a location where it can easily observe the distances and

directions of the features to be mapped.

2. Radiation by Stadia

- Similar to radiation by total station except a stadia is used to determine the features’

distances and elevations.

3. Grid Method

- More commonly used in locating contours instead of features.

- The area being surveyed is staked in squares. The measure of the sides depending on the

ground configuration and the required accuracy. Larger sided squares are used for gentle

slopes while smaller sides are used for rough terrain.

4. Offset from a Reference Line

- Employed in linear features such as roads, rivers, fences.

- A reference line is stationed and perpendicular distances to the feature observed are

recorded as well as the station where they were taken.

5. Topographic Detailing with GPS

- Employs Kinematic GPS Survey

- Provides real time data that can be stored and readily used.

Sources:

Wolf, Paul R., and Charles D. Ghilani. Elementary Surveying: An Introduction to Geomatics. 13th ed.

Upper Saddle River, NJ: Prentice Hall, 2012. Print.

Anderson, J. M., and Edward M. Mikhail. Surveying, Theory and Practice. Boston: WCB/McGraw-Hill,

1998. Print.

Cruz, Anjillyn Mae C. Topographic Surveying. 2015. PowerPoint slides.