A guide to specifying a topographical survey

This guide explains what a topographical survey is, how to specify one properly, and the decisions that determine whether the survey you receive is the survey your project actually needs.

It is written for architects, engineers, planners and developers who need to brief a surveyor and want to avoid the two most common outcomes: paying for detail that will never be used, or discovering mid-design that something essential was never picked up.

What the guide covers

• What a topographical survey is and why the definition matters when you are comparing quotes.
• Setting the control – how survey control is established, and why it is the foundation everything else depends on.
• Ensuring accuracy – what accuracy means in practice and how it is achieved and checked.
• Technology – the equipment used and what each method is suited to.
• Deliverables and formats – the outputs available and which to ask for.
• Spatial Twin – a navigable digital record of the site you can revisit any time.
• 2D plan or 3D model? – choosing the right foundation for your project.
• 2D survey features and 3D deliverables – what is included at each level.
• BIM-ready intelligence and the Revit standard for 3D models.

What should a topographical survey brief include?

Four things decide whether the survey matches the project: the extents, the level of detail, the datum and grid, and the deliverable format. Say where the survey boundary sits and whether it includes anything beyond it, such as adjacent kerb lines or tree canopies. State the level of detail so the surveyor is not guessing. Confirm whether levels are to be tied to OS Datum. And specify the output format you need, including whether a 3D model or Revit file is required, because retro-fitting a model to a 2D survey costs more than capturing for it from the start.

Do I need a 2D plan or a 3D model?

A 2D topographical plan is the right answer for most planning applications, site layouts and drainage design. A 3D model earns its cost when the design is being coordinated in three dimensions, when earthworks volumes matter, or when the survey will feed a BIM workflow. The decision is worth making before the survey, not after: the fieldwork for a model is different from the fieldwork for a plan, and upgrading later usually means going back to site.

About Spatial Dimensions

Spatial Dimensions was established in 2012 and provides measured building surveys, topographical surveys, underground utility surveys and 3D and BIM modelling across the UK. The company carries £10m Professional Indemnity insurance with no claims to date, completes all survey and drafting work in-house, operates an ISO 9001 certified quality management system, holds Once For All health and safety accreditation, and is a corporate member of The Survey Association. Offices in Sevenoaks, London and Nottingham.