Topographic Data

The basic land form (or topographic structure) of a site is first studied by visual inspection. If need arises detailed maps are to be prepared. The following list presents the features of topography, which are important : 

1. Elevation above sea level 
2. Orientation of the site (e.g., east to south-east etc.) 
3. Slopes in percentage (0 to 3%, 3 to 8% etc.) 
4. Surface waters (such as ponds, streams and rivers and drainage patterns) 
5. Hills and valleys (visibility etc.) 
6. Hood plains, swamps, quick sand, etc. 

Topographic Maps 

The contour map is the basis for the preparation of other kinds of topographic maps, as and when found necessary. 

Contour Map of an  Island Drawn from its profile Section 

Contours are sets of imaginary lines that connect all points of same elevation on the ground. The sets of ground points to be connected by these lines (each set of points corresponding to one particular elevation) are separated by some regular interval : 0.25,0.50, or 1 m. Contour lines are always continuous within the space of any one map and do not merge or cross each other except at vertical or over-hanging surfaces. The closer they are together, the steeper the ground is. The more nearly parallel they are, the more regular the ground surface slope prevails. In rolling land, they take the shape of flowing curves; over plane surfaces they run in straight lines. One easily identifies the contour patterns of typical topographic features : stream, valley, ridge, bowl, depression, flat, grade, escarpment, pass, the peak etc. Contours are easily sketched or adjusted to describe the required ground form. An easy familiarity with these patterns is essential for a site planner. 

While contour maps are the standard way of representing ground form, there are other methods. One is to record the spot elevations of key points on the ground : the crests, valley , breaks in grade, floor levels of structures etc. This record may be made more useful by giving the elevation of every intersection point  of some imaginary grid, a method often used for precise calculations in small areas. 

The old method of hachures is still sometimes used in which short lines, perpendicular, rather than parallel to the slope, are drawn side by side the curving runs. Their direction points directly up or down the hill, their length indicates the length of the slope, and their closeness together shows the steepness. They demand skillful drafting. If well done, they give a vivid picture of the general terrain. 

The visual exposure of a single point or the relative exposure of a land area can be analysed and plotted. Figure 1.12 is a single point analysis that displays with dark grid lines areas that can be seen in 360 degrees. When one is standing at a point of observation. Such diagrams have been utilised to locate restaurants and water-towers in hill areas (Joseph De Chiara, et al, 1978). 

Topographic surface, the boundary between earth and air is the richest in living things. It has a particular implication for site development. The gradient of paths, the flow of utilities, the use of areas, the disposition of buildings and the visual aspect are all affected by it. The designer must grasp the character of the land form as a whole and identity its key points for the purpose he has in mind. In most cases, the existing topography has an underlying order brought about by the flow of surface water (Kevin Lynch, 1971). 

Slope can be classified according to their potential use, such as, a flat ground, can be used for intensive activity. Slopes over 10 percent require considerable effort to climb; and to erect buildings on them, more complicated form and foundations and more difficult utility connections are required. 

Another critical aspect of ground form is the way in which it limits orientation by means of roads, gravity based utilities, such as sewers. Grades under 1 percent are difficult to drain naturally by gravity.