What Is A Topographical Survey? A Beginners Guide To What, Why & How.
Tom Ayre – Company Director
THS Concepts LTD
A topographical survey measures and identifies natural and manmade features within an area of land. Topographical surveys are usually required by architects and engineering companies when land is being developed or altered. This includes projects such as new buildings, civil engineering projects, repurposing land use, etc.
Topographical surveys are undertaken by land surveying companies using a range of different survey equipment that can measure distances and angles extremely accurately. Using the equipment helps to produce a CAD (computer-aided design) drawing that accurately positions surveyed points in both plan and height.
Often precise GPS survey equipment is utilised to locate and position fixed points on an area of land. These points are used as reference markers, which allow the surveyed area of land to be aligned on to an existing national coordinate system in both plan and height. In the UK the most common national coordinate system used in land surveying is OSGB36.
Example of a Topographical Survey
Why Do You Need a Topographical Survey?
A topographical survey is useful when working on a design for a land development projects as it will help correctly plan out and coordinate the proposed layouts. With the information from the survey you can to see exactly how the existing site is arranged, including positions and associated heights of items. Useful applications for topographical surveys include:
- Repositioning boundaries Knowing the exact location of boundaries is helpful as you may need to build a new building that is exactly x distance away from a boundary that may have been removed
- Planning new buildings Knowing where items on site such as trees, buildings, power lines, etc. is helpful as you can position your building correctly, thus avoiding future problems
- Correctly designing drainage schemes You will have the heights of the land and water features on site that need to be tied into.
What Is Surveyed?
A topographical survey can be as extensive as required. Usually, a client will have a good idea of what information they require from the survey. This is usually specified when instructing a surveying company to undertake the survey work. For instance, if you are working on repositioning boundary fences, survey items such as tree locations, or inspection chambers may not be required.
A typical topographical survey when developing an area of land for building work picks up items such as:
- Boundary locations
- Building positions
- Change in surfaces
- Drains & invert levels
- Inspection chambers (water, gas, electricity etc)
- Kerb positions
- Overhead lines (power, telephone etc)
- Ridge & eaves heights of buildings
- Spot heights of the land
- Street furniture (bins, post boxes etc)
- Tree locations with spread & trunk diameter.
- Water features (ponds, waterways etc)
Total Station on a Topographic Survey
What Information Can A Topographic Survey Produce?
Following the site survey, a range of information and drawings can be produced. This includes:
- Drawings Plans, elevations, sections, street scenes, lighting plans etc. Drawings in CAD / PDF format
- 3D Point Clouds Data useful to build a 3D model of the site in a program such as Autodesk Revit
- Photographs Useful for people looking for information about the site
- Schedules Information such as inspection chamber inverts, pipe diameter sizes, etc. can be produced
How Are Topographical Surveys Undertaken On Site?
A topographical survey is usually undertaken by a team of experienced surveyors, armed with equipment including total stations, GPS equipment, laser measurement devices and tape measures. A total station is a tripod mounted device used by surveyors to accurately plot single points which can be joined into lines and arcs to form a drawing of a site.
The survey begins with the surveying team placing their fixed setting out marker points using the GPS and total stations. The fixed markers usually come in the form of survey nails secured into solid ground (concrete, brick etc) or reflective tape targets fixed to walls.
Reflective Survey Target
These reference points are used to recalculate the position of the survey equipment as it moves around the site. They are vital for allowing the survey to be “stitched” together correctly from one set-up position to the next.
Once set up, the survey can begin. Using a total station in combination with taking notes and hand measurements, the surveyor will begin to record data. The total station uses laser technology to accurately record positions points in plan and height. Using a combination of 2 points, a line can be drawn on the total station in order to begin building up a detailed picture. A good example is taking a point on either end of a wall and drawing a line between the two.
In some instances, it may be required to use a prism mounted on a pole to pick up features. Using a modern robotic total station as the base unit, a surveyor can move around the site with the total station turning to follow as they move. Additionally, the surveyor can use a wireless computer unit to take points without looking through the lens of the total station. This feature is useful as it allows 1 person to operate, thus making the process a lot more efficient.
A Survey Nail
How Are Topographical Surveys Produced in the Office?
Once the required information has been recorded on site, the surveyor returns to their office to draw up the survey using CAD. The most popular CAD software to use is AutoCAD produced by Autodesk, although there are many others in the market including Bentley Microstation & SketchUp.
The recorded data is exported from the total station/GPS equipment and saved onto a computer. The surveyor uses CAD software to begin tidying up and producing a plan view drawing of the land. The process usually involves joining lines together such as the corners of buildings or adding symbols such as trees. Height markers will also be added showing the levels of important elements such as the ground, building ridge heights, watercourse levels etc.
Once the base plan drawing has been produced, the surveyor begins to produce other drawings such as elevations and sections of the site. Once all drawings have been completed, the surveyor will ask for a final check by a colleague before sending the CAD drawing and associated PDFs to the client. The client may give feedback to where additional detail may be required or where details can be relaxed. Drawings may be revised before the final copy is agreed.
Topographical Survey CAD Drawing
What To Check When Hiring a Land Survey Company
When appointing a land surveyor it’s important you choose the right company to avoid future problems as a result of poor drawings and communication. Prior to appointment, we recommend checking the following:
Experience Land Surveying is a complicated task. Surveyors are required to operate complex survey devices and then produce clear, accurate drawings to be presented to the client. An experienced survey team has the knowledge to avoid problems and get the work completed efficiently and to a high standard.
Size of company Sometimes a “one man band” company is perfect for your requirements. On balance, however, this can cause problems with getting answers quickly, revisiting the site etc. Furthermore, a company with only 1 or 2 employees may leave clients waiting as they are regularly out of the office, unavailable to talk or not around to check or reissue drawings.
Insurances When things go wrong, there can be serious financial implications. Check your land surveying company has the correct professional indemnity insurance for their work and that the cover they provide is more than suitable for your requirements. A reputable company should also carry employer’s liability and public liability insurance.
General feel Do employees present themselves in a professional manner? Usually, gut instinct is helpful to get a feel for how easy it will be to work with a company. Red flags that raise suspicions include:
- No address on the website Can surveyors be tracked down if things go wrong? A survey company should not be operating from a PO box, for instance
- Much cheaper than others Like most things in life, you pay for what you get. A very low quote in comparison to other companies may result in poor workmanship and customer service
- Telephone/email manner Are your phone and email messages answered promptly? If not then this may reveal an overworked/understaffed company
- Poorly designed website This is usually a sign of a company who aren’t very technology savvy or aren’t too interested in the user experience on site
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Example of a Topographical Survey