A topographic survey is the map your architect and civil engineer design on. If it is incomplete, every downstream drawing inherits the gaps. Here is what each deliverable actually is, which format your team needs, and why how the site was captured matters more than most people realize.
Contours
Contours are lines of equal elevation — the familiar topographic "rings." The key spec is the interval:
- 1-foot interval — the standard for residential design work in the East Bay. Enough resolution for drainage, grading, and foundation design on most lots.
- Half-foot interval — flat sites where drainage is critical; small elevation changes decide which way water flows.
- 2-foot interval — steep hillside sites where 1-foot lines would blur into solid ink; often paired with dense spot elevations.
Contours are generated from the terrain model, not measured directly — which means their quality is only as good as the surface beneath them.
DTM vs. DSM: Two Different Surfaces
- A DTM (digital terrain model) is the bare ground — vegetation, cars, and structures stripped away. This is what grading and drainage design uses.
- A DSM (digital surface model) includes everything the sensor saw — rooflines, tree canopy, walls. Useful for view studies, solar analysis, and context modeling.
Producing a trustworthy DTM on a brushy East Bay hillside is real work: the ground must be separated from ivy, brush, and canopy. High-density laser scanning helps here — with millions of points, enough of them reach true ground through gaps in vegetation to build a reliable surface, something sparse conventional shots cannot guarantee.
Spot Elevations and Break Lines
Spot elevations are individual labeled grades at points that matter: finish floors, top and bottom of walls, curbs, drainage inlets, driveway crests. Break lines define where the surface changes slope abruptly — top and toe of banks, wall lines, curb lines. A terrain model without correct break lines rounds off exactly the edges your engineer cares about.
The Point Cloud
When a site is captured with a terrestrial laser scanner, the raw deliverable is a point cloud — millions of measured 3D points covering everything visible: terrain, structures, walls, trees, utilities. The CAD map is extracted from it, but the cloud itself is deliverable too, in E57 (open standard) or RCP (Autodesk ReCap) format. Design teams use it to answer questions the flat map never anticipated — "how tall is that wall?", "what's the clearance under that deck?" — without anyone driving back to the site.
File Formats
| Format | What It's For |
|---|---|
| DWG / DXF | The layered CAD base map — what architects and civil engineers design on |
| LandXML | The terrain model itself, importable into Civil 3D and other design software |
| E57 / RCP | Point cloud for design-team reference and modeling |
| Stamped record copy for permit submittals |
Why the Capture Method Decides the Quality
A conventional topo crew measures one point at a time with a total station — a few hundred shots on a typical lot. Every contour and grade on the map is interpolated between those shots. Miss a grade break, a wall face, a swale? The map is wrong there, and nobody finds out until design or construction hits it.
Our Trimble terrestrial laser scanner captures the same site as millions of survey-grade points in one visit. The deliverables are extracted from complete data: contours from a fully-measured surface, spot grades from real points rather than interpolation, and a point cloud that keeps answering questions after fieldwork ends. One mobilization, no return trips, no "we didn't shoot that."
Details and typical scopes on our topographic survey service page.