Drone mapping can produce several different types of elevation data, and two of the most common are Digital Terrain Models (DTMs) and Digital Surface Models (DSMs). While the terms sound similar, they represent different information about a project site.
Understanding the difference is important when determining which dataset is appropriate for applications such as topographic mapping, grading, drainage, construction planning, and earthwork.
What Is a Digital Terrain Model (DTM)?
A Digital Terrain Model (DTM) represents the elevation of the underlying ground surface. Above-ground features such as buildings, trees, and other structures are generally removed or filtered from the dataset so that the model focuses on the terrain itself.
For construction and land development projects, this can make a DTM particularly useful when the goal is to understand the actual shape and elevation of the ground.
DTMs can support applications such as:
- Topographic mapping
- Grading and site design
- Drainage analysis
- Cut-and-fill analysis
- Earthwork planning
- Land development
In simple terms, a DTM answers the question:
“What does the ground look like without the features sitting on top of it?“
What Is a Digital Surface Model (DSM)?
A Digital Surface Model (DSM) represents the elevation of the surfaces captured by the mapping system—including the ground as well as features above it.
Depending on the site, a DSM can include buildings, trees, vegetation, equipment, stockpiles, and other structures or objects.
This makes DSMs useful when the project team needs to understand the entire surface environment, rather than just the bare earth.
Common applications include:
- Construction progress documentation
- Vegetation and site analysis
- 3D visualization
- Building and structure mapping
- Site documentation
- Surface feature analysis
A DSM answers a slightly different question:
“What does the surface of the site look like, including the features on top of the ground?“
DTM vs. DSM: What’s the Difference?
The easiest way to understand the difference between a DTM and DSM is to think of bare earth versus the entire surface. A DTM focuses on the underlying ground and typically filters out features such as buildings, trees, and vegetation. This makes it useful for applications where terrain and elevation are the primary concern, such as grading, drainage, topographic mapping, and earthwork.
A DSM, on the other hand, represents the surface as it exists, including above-ground features. Depending on the site, this can include buildings, trees, vegetation, equipment, stockpiles, and other structures. Because of this, DSMs can be useful for site documentation, 3D visualization, construction progress monitoring, and analyzing surface features.
In simple terms, a DTM shows you the shape of the ground, while a DSM shows you the surface of the site, including the features on top of it. The right option depends on what your project needs to measure, analyze, or document.
DTM vs. DSM: It’s About the Project
There isn’t one surface model that is automatically better than the other.
A grading project may need a DTM to understand existing ground elevations, while a construction documentation project may benefit more from a DSM that captures buildings and other features. Other projects may benefit from having both datasets available.
The key is identifying what information the project team needs before selecting the final deliverables.
Final Thoughts
DTMs and DSMs both provide valuable elevation information, but they serve different purposes.
A DTM focuses on the underlying terrain, while a DSM represents the surface, including above-ground features. Understanding that distinction can help engineers, contractors, developers, and project owners choose the right mapping deliverables for their project.
At Summit LiDAR, we provide drone LiDAR, topographic mapping, DTMs, DSMs, orthomosaics, and other geospatial deliverables for construction, land development, engineering, and other projects across Colorado.
