Visualizing Topographic Contours in Google Earth

Introduction

In this tutorial, you will learn how to visualize topographic contours over a 3D terrain using Google Earth. This process involves downloading digital elevation data, generating contour lines with QGIS, and visualizing these contours in Google Earth. By the end of the tutorial, you'll have a clear understanding of how to create and visualize topographic contours, enhancing your geographic data analysis.

Step 1: Download SRTM Digital Elevation Data

To start, you need to download the SRTM (Shuttle Radar Topography Mission) digital elevation data from the USGS EarthExplorer web portal.

1. Visit the USGS EarthExplorer website.
2. Create an account or log in if you already have one.
3. Use the search tool to define the area of interest by:
   • Entering coordinates or searching by location name.
   • Drawing a bounding box on the map.
4. On the left sidebar, select the "Data Sets" tab.
5. Expand the "Digital Elevation" category and choose "SRTM."
6. Click on the "Results" button to view available datasets.
7. Select the desired dataset and click on the download option.

Practical Tip

Ensure you choose the correct resolution based on your project's requirements. The 30m resolution is commonly used for detailed analysis.

Step 2: Generate Contour Lines Using QGIS

Once you have the elevation data, you'll need to use QGIS to generate contour lines.

1. Open QGIS on your computer.
2. Import the downloaded SRTM raster file:
   • Go to "Layer" > "Add Layer" > "Add Raster Layer."
   • Browse to your downloaded SRTM file and open it.
3. Generate contour lines:
   • Go to "Raster" > "Extraction" > "Contour."
   • Set the following parameters:
     • Input layer: Select your SRTM layer.
     • Interval: Define the contour interval (e.g., every 10 meters).
     • Output file: Choose a location to save the contour lines as a shapefile.
4. Click "Run" to generate the contour lines.

Common Pitfall to Avoid

Make sure your contour interval is appropriate for the terrain. A very small interval can create too many lines, making it cluttered and hard to read.

Step 3: Export Contour Lines to KML Format

After generating the contours, you need to export them to a KML file for use in Google Earth.

1. Right-click on the contour layer in the Layers panel.
2. Select "Export" > "Save Features As."
3. In the format dropdown, choose "Keyhole Markup Language [KML]."
4. Specify the output file name and location.
5. Click "OK" to save the file.

Practical Tip

Ensure that the coordinate reference system (CRS) is set to WGS 84 to ensure compatibility with Google Earth.

Step 4: Visualize Contours in Google Earth

Now that you have your KML file, you can visualize the contours in Google Earth.

1. Open Google Earth on your computer.
2. Go to "File" > "Open," and select the KML file you exported.
3. The contour lines should now be visible over the 3D terrain.
4. Use the navigation tools to explore the contours from different angles and perspectives.

Real-World Application

This technique is useful for various applications, including urban planning, environmental studies, and educational purposes.

Conclusion

In this tutorial, you learned how to download digital elevation data, generate contour lines using QGIS, and visualize them in Google Earth. This process enhances your ability to analyze and present geographic data effectively. For further exploration, consider watching related tutorials on using Google Earth and QGIS for added insights and functionalities.