Working with Terrain Data in QGIS

Download, process, visualize, and analyze elevation data using QGIS

A comprehensive guide to downloading terrain data from USGS, extracting contour lines, creating cross-sections, and 3D visualizations in QGIS

Tutorial: Working with Terrain Data in QGIS

Master the art of downloading, processing, and visualizing elevation data for professional GIS analysis.

90 minutes

Intermediate

GIS Geospatial QGIS

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Learning Objectives

By the end of this tutorial, you will be able to:

• Download elevation data from USGS EarthExplorer
• Process and merge multiple raster tiles into a single DEM
• Extract contour lines from elevation data
• Create cross-sections to visualize terrain profiles
• Produce 3D visualizations of terrain using QGIS plugins

These skills are essential for terrain analysis, watershed modeling, and environmental planning.

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Workflow Summary

This tutorial follows these key steps:

┌─────────────────────────────────────────────────────┐
│ STEP 1: Download & Prepare Data                     │
│ What: Acquire terrain data from USGS                │
│ Time: ~20 min                                       │
└──────────────────────┬──────────────────────────────┘
                       ↓
┌─────────────────────────────────────────────────────┐
│ STEP 2: Extract Contour Lines                       │
│ What: Create elevation contours from raster         │
│ Time: ~25 min                                       │
└──────────────────────┬──────────────────────────────┘
                       ↓
┌─────────────────────────────────────────────────────┐
│ STEP 3: Create Cross-Sections                       │
│ What: Generate terrain profile graphs               │
│ Time: ~20 min                                       │
└──────────────────────┬──────────────────────────────┘
                       ↓
┌─────────────────────────────────────────────────────┐
│ STEP 4: 3D Visualization                            │
│ What: Create interactive 3D terrain views           │
│ Time: ~25 min                                       │
└──────────────────────┬──────────────────────────────┘
                       ↓
┌─────────────────────────────────────────────────────┐
│ RESULT: Complete terrain analysis package           │
└─────────────────────────────────────────────────────┘

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Prerequisites & Requirements

Before you start, make sure you have:

• QGIS 3.x or higher installed (free download from qgis.org)
• Internet connection to access USGS EarthExplorer
• Free USGS account (registration required)
• Study area shapefile (provided or create your own)
• Disk space for elevation data (~500 MB for typical study areas)

Knowledge assumed: - Basic QGIS interface familiarity - Understanding of shapefiles and projections - Comfort with raster and vector data concepts

⚠️ Important: The USGS EarthExplorer requires free registration. Create your account before starting this tutorial.

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Data & Resources

Key resources you’ll need:

Resource	Source	Purpose
USGS EarthExplorer	https://earthexplorer.usgs.gov	Download SRTM elevation data
Study Area Shapefile	Provided in tutorial materials	Define your area of interest
QGIS Plugins	Built-in Plugin Manager	Profile Tool, Qgis2threejs

Optional supporting resources: - USGS Documentation: https://lpdaac.usgs.gov - SRTM Dataset Info: https://earthexplorer.usgs.gov - QGIS Manual: https://docs.qgis.org

⚠️ Registration required: Create a free USGS account at https://earthexplorer.usgs.gov

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Step-by-Step Instructions

Step 1: Download & Prepare Terrain Data

What you’ll do: Access USGS EarthExplorer, upload your study area, and download SRTM elevation data tiles.

1.1 - Register and Access USGS EarthExplorer

Create a free USGS account and log in to the EarthExplorer platform. This is a critical first step as you cannot download data without authentication.

Navigation Steps

1. Visit <https://earthexplorer.usgs.gov/
2. Click “Register” (if you don’t have an account)
3. Fill in your details and verify your email
4. Log in with your credentials

1.2 - Prepare and Upload Your Study Area

Before downloading data, you need to define the extent of your area of interest. You’ll convert your shapefile to KML format and upload it to EarthExplorer.

In QGIS:

QGIS Menu Sequence

Layers Panel → Right-click "study_area" layer 
  → Export → Save Layer As...

This opens the export dialog. Configure as follows:

• Format: Keyhole Markup Language [KML]
• Filename: Study_area.kml
• CRS: Keep default (WGS 84)
• Click OK

On EarthExplorer Website:

Web Browser Steps

Search Criteria 
  → KML/Shapefile Upload 
  → Select File 
  → Choose your Study_area.kml

The map will update to show your study area boundary (typically highlighted in blue or green).

1.3 - Search and Download SRTM Data

Now search for elevation data within your study area boundaries.

Search for SRTM Data:

SRTM Data Search Process

Data Sets 
  → Search "Digital Elevation" 
  → Select "SRTM 1 Arc-Second Global" 
  → Click Results

The system will display available tiles that intersect your study area. You’ll typically see 2-4 tiles depending on your area size.

Review and Download:

• Preview Click the foot icon to see each tile’s extent
• Select Format Choose GeoTIFF 1 Arc-second
• Download Download all tiles that cover your area

Save the GeoTIFF files to a dedicated folder (e.g., data/elevation_raw/)

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Step 2: Process and Merge Elevation Data

What you’ll do: Merge multiple raster tiles into a single DEM and reproject to your working coordinate system.

2.1 - Build Virtual Raster

The downloaded SRTM data comes as separate tiles. First, create a virtual raster that merges them.

In QGIS:

QGIS Raster Menu

Raster 
  → Miscellaneous 
  → Build Virtual Raster

Configuration:

Parameter	Setting
Input layers	All 4 SRTM tiles
Place each input file into a separate band	☐ Unchecked
Allow projection difference	☑ Checked
Nodata value	-9999
Output file	dem_virtual.vrt

Click Run to merge the tiles into a single virtual raster.

2.2 - Reproject to UTM Coordinates

The SRTM data is in geographic coordinates (WGS 84). Reproject it to a projected coordinate system for accurate area-based analysis.

QGIS Raster Menu

Raster 
  → Projections 
  → Warp (Reproject)

Configuration:

Parameter	Setting
Input layer	dem_virtual.vrt
Target CRS	WGS 84 / UTM zone 32 N
Output file	dem_reprojected.tif

Note: Adjust the UTM zone based on your location (32N for Europe, etc.)

2.3 - Clip to Study Area

Extract only the data for your study area to reduce file size and processing time.

QGIS Raster Menu

Raster 
  → Extraction 
  → Clip Raster by Extent

Configuration:

Parameter	Setting
Input layer	dem_reprojected.tif
Clipping extent	Use Layer Extent → study_area
Nodata value	-9999
Output file	dem_clipped.tif

Your processed DEM is now ready for analysis!

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Step 3: Extract Contour Lines

What you’ll do: Generate contour lines from the elevation raster to visualize terrain topology.

3.1 - Apply Gaussian Filter (Optional but Recommended)

The Gaussian filter smooths the elevation data, creating cleaner, more aesthetically pleasing contour lines by removing noise.

QGIS Processing Toolbox

Search for “Gaussian filter” in the Processing Toolbox.

Configuration:

Parameter	Setting
Grid	dem_clipped.tif
Search Mode	Circle
Standard Deviation	1.0 (default)
Output file	dem_clipped_gauss.tif

Click Run. The result is a smoothed elevation model.

3.2 - Generate Contour Lines

Now create vector contour lines from your elevation data.

QGIS Raster Menu

Raster 
  → Extraction 
  → Contour (Vector)

Configuration:

Parameter	Setting	Notes
Input layer	dem_clipped.tif	Use original or smoothed DEM
Interval between contours	10	Meters (adjust for your area)
Output file	contour_lines_10m.shp	Vector shapefile
Attribute name	elevation	Field storing elevation values

Click Run. You now have contour lines showing terrain elevation!

Pro Tip: For larger areas (>1000 km²), use a 20 or 25m interval to avoid overcrowding. For smaller areas (<100 km²), 5m intervals provide good detail.

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Step 4: Create Cross-Sections

What you’ll do: Install the Profile Tool plugin and create terrain elevation profiles.

4.1 - Install Profile Tool Plugin

The Profile Tool creates interactive terrain cross-sections that show elevation changes along a line.

In QGIS:

QGIS Plugin Menu

Plugins 
  → Manage and Install Plugins

In the Search box: - Type: “Profile tool” - Select: “Profile tool” (by Borys Jurgiel) - Click: Install Plugin

Wait for installation to complete, then click OK.

4.2 - Activate and Configure Profile Tool

QGIS Menu Sequence

Plugins 
  → Profile tool 
  → Terrain profile

A new Profile panel appears on the right side of QGIS.

Setup:

1. In the Layers panel, select your DEM raster
2. In the Profile panel, click “Add Layer”
3. Select “Temporary polyline” (or “Active layer polyline”)
4. On the map, draw a line across the terrain where you want the cross-section

The elevation profile graph appears automatically in the Profile panel!

Customize the Graph:

• Right-click the graph to access export and configuration options
• Adjust Y-axis to emphasize terrain relief
• Export as PNG, PDF, or SVG for reports

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Step 5: 3D Visualization

What you’ll do: Install Qgis2threejs plugin and create interactive 3D terrain views.

5.1 - Install Qgis2threejs Plugin

This plugin generates stunning 3D visualizations of your terrain data.

In QGIS:

QGIS Plugin Menu

Plugins 
  → Manage and Install Plugins

In the Search box: - Type: “Qgis2threejs” - Select the plugin by Minoru Akagi - Click: Install Plugin

The plugin installation may take 30-45 seconds. Click OK when complete.

5.2 - Create 3D Terrain View

Once installed, a new Web toolbar appears above your map.

QGIS Qgis2threejs Menu

Web 
  → Qgis2threejs 
  → Qgis2threejs Exporter

Configuration:

1. DEM layer: Select dem_clipped.tif
2. Color layer: Optional (use contour_lines for additional detail)
3. Vertical exaggeration: 1.5-2.0 (exaggerates relief for visibility)
4. Export format: HTML (for web) or Three.js (for advanced use)
5. Output filename: terrain_3d.html

Click Export. Your 3D visualization opens in a web browser!

Interact with 3D view: - Rotate Click and drag - Zoom Scroll wheel - Pan Right-click and drag

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Result & Expected Outcome

What you should have now:

✅ Processed DEM ready for analysis
✅ Vector contour lines showing terrain topology
✅ Terrain cross-sections for elevation profiles
✅ Interactive 3D visualization for presentations

Your final data package includes:

study_area_terrain/
├── raw_data/
│   ├── SRTM_tile_N50_E005.tif
│   ├── SRTM_tile_N50_E006.tif
│   ├── SRTM_tile_N51_E005.tif
│   └── SRTM_tile_N51_E006.tif
├── processed/
│   ├── dem_virtual.vrt
│   ├── dem_reprojected.tif
│   ├── dem_clipped.tif
│   └── dem_clipped_gauss.tif
├── vectors/
│   ├── contour_lines_10m.shp
│   ├── contour_lines_10m.dbf
│   ├── contour_lines_10m.shx
│   └── contour_lines_10m.prj
├── visualizations/
│   ├── terrain_profile_section_A.png
│   ├── terrain_profile_section_B.png
│   └── terrain_3d.html
└── analysis_results/
    ├── elevation_statistics.csv
    └── slope_analysis.tif

What you can do next: - Perform slope and aspect analysis - Calculate watershed boundaries - Model hydrological flows - Plan infrastructure projects - Generate professional map layouts

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Exercises & Challenges

Challenge 1: Intermediate - Extract Multiple Contour Intervals

🟡 Create Multi-Scale Contours Intermediate

Objective: Create contour maps at different intervals to understand when each is appropriate.

Your task:

1. Generate contour lines at 5m interval and save as contour_5m.shp
2. Generate contour lines at 25m interval and save as contour_25m.shp
3. Compare both visually in QGIS
4. Document which is better for your area and why

Hint: Use smaller intervals for detailed small-area analysis, larger intervals for regional overviews.

Solution (click to reveal):

Tip

For 5m contours:

Raster > Extraction > Contour
Input: dem_clipped.tif
Interval: 5
Output: contour_5m.shp

For 25m contours:

Raster > Extraction > Contour
Input: dem_clipped.tif
Interval: 25
Output: contour_25m.shp

Comparison: The 5m contours show detailed terrain variation ideal for engineering and detailed planning. The 25m contours are clearer for regional analysis and printed maps.

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Challenge 2: Intermediate - Calculate Slope from DEM

🟡 Slope and Aspect Analysis Intermediate

Objective: Derive slope and aspect rasters from the DEM for terrain analysis.

Your task:

1. Use Raster > Analysis > Slope on your DEM
2. Use Raster > Analysis > Aspect on your DEM
3. Apply a color ramp to visualize slope categories
4. Identify areas of steep terrain (>30°)

Resources: - QGIS Raster Analysis: <https://docs.qgis.org/latest/en/docs/user_manual/processing_algs/qgis/rasteranalysis.html

Hint: Slope values >30° indicate steep terrain unsuitable for building but good for hydropower studies.

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Tips, Tricks & Warnings

💡 Pro Tips

• Tip 1: Check data resolution - SRTM 1 Arc-Second has ~30m resolution. For smaller areas, consider ASTER GDEM (higher resolution) or LiDAR data.

• Tip 2: Use virtual rasters - Building virtual rasters (VRT) keeps original data intact and processes faster than creating new files.

• Tip 3: Smooth before contouring - Always apply a Gaussian filter before extracting contours. Smoothing removes noise artifacts and creates professional-looking contour maps.

• Tip 4: Exaggerate vertical scale in 3D - Use 1.5-2.0x exaggeration in 3D visualizations to make subtle terrain variations visible in presentations.

• Tip 5: Cache your processed data - Save clipped, reprojected DEMs so you don’t need to re-download raw tiles every time.

⚠️ Common Pitfalls

Watch out for these mistakes:

1. Forgetting to reproject: SRTM data is in WGS 84 (geographic). Always reproject to UTM or local coordinates before analysis to get accurate measurements.

   ❌ Measuring in degrees = inaccurate distances
   ✅ Measure in UTM = accurate meters/kilometers

2. Wrong contour intervals: Using 10m contours for a 100 km² region creates thousands of lines. Use 25-50m for large areas.

3. Not checking Nodata values: SRTM often has -9999 for water bodies. Specify this or your analysis will be corrupted by these artificial values.

4. Ignoring edge effects: Clipped DEMs have edge artifacts. Keep a buffer around your actual study area when downloading.

🔴 Critical Warnings

These mistakes could corrupt your analysis:

⚠️ Always backup original SRTM tiles before processing. Download once, work with copies:

# Recommended directory structure
├── data_original/          ← Original SRTM (never modify)
│   └── SRTM_*.tif
└── data_working/          ← Your processed versions
    ├── dem_virtual.vrt
    ├── dem_reprojected.tif
    └── dem_clipped.tif

⚠️ Verify your projection before publishing maps. Mistakes here are costly:

Check: Raster > Properties > Source 
✅ Verify CRS shows "WGS 84 / UTM zone 32 N"
❌ Do NOT report results if CRS is uncertain

⚠️ Test contour extraction on small areas first before processing entire datasets. A failed 500MB process wastes hours.

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Related Tutorials & Next Steps

After completing this tutorial, you might be interested in:

Level Up Your Skills

1. Advanced Terrain Analysis: Hydrology & Watersheds - Delineate drainage basins and flow paths
   • Estimated time: 60 minutes
   • Difficulty: Advanced
2. LiDAR Data Processing in QGIS - Work with high-resolution LiDAR point clouds
   • Estimated time: 90 minutes
   • Difficulty: Advanced
3. Geological Mapping & Cross-Sections - Create professional geological cross-sections from DEM data
   • Estimated time: 45 minutes
   • Difficulty: Intermediate

Related Topics

• Hillshade & Slope Mapping - Visualize terrain with shaded relief
• Viewshed Analysis - Calculate visible areas from observation points
• Aspect & Curvature - Analyze terrain orientation and landform classification
• Land Cover Classification from Terrain - Combine DEM with other data for analysis

Practice Projects

• Project 1: Create a professional terrain map of your local area
• Project 2: Analyze a watershed using derived terrain products
• Project 3: Design a hiking trail using slope and contour analysis

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References & Further Reading

Official Documentation

• QGIS Manual: https://docs.qgis.org/latest/en/docs
  • Raster Analysis Tools
  • Raster Extraction Tools
• USGS EarthExplorer: https://earthexplorer.usgs.gov
  • SRTM Dataset Documentation
  • Data Access Guide

Tutorials & Guides

1. “QGIS Raster Analysis” - QGIS Documentation (Official)
   • Comprehensive guide to raster processing tools
   • Available: https://docs.qgis.org/
2. “SRTM Data and Terrain Analysis” - USGS Guide (2020)
   • Technical specifications and best practices
   • Available: https://lpdaac.usgs.gov/

Plugin Documentation

• Profile Tool Plugin: https://github.com/borisj/ProfileTool
  • GitHub repository with examples and troubleshooting
• Qgis2threejs Plugin: https://qgis2threejs.readthedocs.io/
  • Complete documentation with advanced 3D options

Related Datasets

• SRTM Data: 30m resolution global elevation (what you’re using)
• ASTER GDEM: Higher resolution (15m) alternative
• GEBCO Bathymetry: For coastal/ocean terrain
• National LiDAR: Country-specific higher resolution data

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Questions or Issues?

If you encounter problems:

1. Check QGIS compatibility - Ensure you’re running QGIS 3.0 or newer
2. Verify USGS account - Registration required for all downloads
3. Check internet connection - EarthExplorer requires stable connection
4. Search QGIS Documentation - https://docs.qgis.org/
5. Ask on GIS Stack Exchange - https://gis.stackexchange.com/

Common issues:

Issue	Solution
Plugin won’t install	Update QGIS to latest version
“Nodata” artifacts in contours	Check nodata value is set to -9999
3D visualization very slow	Use larger contour intervals (25-50m)
Projection mismatches	Always reproject to UTM before analysis

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Tutorial Version: 1.0
Last Updated: February 5, 2025
Difficulty: Intermediate
Estimated Duration: 90 minutes
Status: ✅ Complete and tested in QGIS 3.28.0