What is topographical survey or topographical map?
Any industrial plants or building and even when we are planning to build new house, we should know about the land details. Question is “why it is required?” Why not we can directly build the house or plant on open area. But unfortunately this is not the correct way. I will explain you why it is required, suppose you start building a construction, and lately during excavation you understand that, there are buried sewage pipelines or drainage or electrical cables below open area, then this will be big impact in terms of cost, planning, time delay etc. Hence, to avoid any surprises and avoid sudden impact, we should know where are nearby utilities and other buried infrastructures like sewers, drains and water pipes are located underground.
Second question comes in mind, “then how we can able to know these details for open area or land?.” A answer is “topographical survey” or “topographical survey map”.
Topographical survey report or map will give you brief information about your open area or land before starting construction on it, so that you can do proper design of building or any plant and all things are clear.
A topographic survey locates all surface features of a open area, and provides all actual features and levels or elevations in terms of contours. We can call it as a 3D map of a 3D land showing all actual including artificial features and renovations. Mainly, it shows location, size, height and any changes in elevation.
Why is topographical survey or topographical map is required?
This is already explained in detail is above section. To summarise topographical survey or maps are important as they provide all details around your open area or land including buried or underground information. In addition to this, we will get information about the land slops, highs, lows and to understand if we have to plan for drainage or water system to building or plant.
Mainly topographical survey will be carried our by civil stream, at site level using many relevant machines and tools.
Next step is how it was done?
First step of to carry out plan surveying. The purpose of the this survey is to get, on a horizontal plane, the position of one or more points in relation to the position of one or more other points. To do this, you will measure horizontal distances and horizontal angles or directions.
Direct levelling is the second step of survey. The purpose of the second survey is to find vertical height or the elevation of one or more than one points above a definite horizontal plane. To do this, you will measure horizontal distances and height differences; you may also need to lay out contour lines.
Refer above Image 1, which shows different contours with different points interconnected with elevations. Company to company above Survey maps may change, based on their requirements.
Reading topographical survey or topographical map?
Topographical survey or map consists of grids marked for selected area or land with coordinates. Refer below snap for reference.
All symbols and legends are indicated in topographical map. For reference below snap is uploaded.
In addition to above information, topographical survey report indicates coordinates on all corners of selected topo area with its surveyed elevations.
Each contour indicated with have points connected with elevations indicated at each point, this will represent if any issues in case of rain fall based on level differences. During survey if any underground services found will be indicated in survey report or map as per above legend or symbols. These legends may change company to company.
Topographical Survey Report or Map Important Points
- Level change or slopes – When level change is sudden with steep slope, contour lines are close to each other, and subsequently slope becomes uniform.
- Water Flow and its source – Water flow direction will be judged based on V points pointing towards source of water. When crossing river, creek, wadis, contour lines bend upstream and form a V.
- Hills or high elevations mountains – We can see if contours are circles and get closer and smaller, then this point is high elevation with hills or mountains.
- Highest possible elevation – The highest possible elevation is just below the value of what the next contour line would be.
- Depressions – Hatch marks are provided on survey map for land dips down.
- Lowest possible elevation of a depression – The first hatched line is the same elevation as the previous contoured line. That means that the lowest possible elevation of a depression is just above the value of what the next contour line would be.
This is all about basic information about trophological survey report or map.
