If you need a quick estimate of terrain slope, Google Earth Pro can help you obtain elevation and distance information along a path. Its elevation profile displays elevation on the vertical axis and distance along the path on the horizontal axis, making it useful for examining changes in terrain.
However, Google Earth Pro should generally be treated as a planning and preliminary analysis tool, rather than a replacement for a professional topographic survey.
What Is Slope?
Slope describes the change in elevation relative to horizontal distance. It is commonly expressed as a percentage:
Slope (%) = (Elevation Difference ÷ Horizontal Distance) × 100
For example, suppose two points have an elevation difference of 20 metres and a horizontal distance of 200 metres:
Slope = (20 ÷ 200) × 100 = 10%
This means the terrain rises or falls by approximately 10 metres for every 100 metres of horizontal distance.
The direction also matters. If the second point is higher, the slope is uphill; if it is lower, the slope is downhill.
Step 1: Create a Path in Google Earth Pro
Open Google Earth Pro and navigate to the area you want to analyse.
Use the Add Path tool to draw a line between the points or along the route you want to investigate. For a relatively simple slope calculation, place the first point at the beginning of the section and the final point at the end.
Google Earth allows you to create paths and subsequently examine their distances and other information.
For terrain analysis, draw the path as close as possible to the actual route, road, drainage channel, or proposed alignment you are studying.
Step 2: Open the Elevation Profile
Google provides official instructions on using measurements and elevation profiles in Google Earth Help — Measure Distance & Elevation.
After creating or selecting the path, use:
Edit → Show Elevation Profile
Google Earth Pro will display an elevation profile in the lower part of the 3D Viewer. The Y-axis represents elevation, while the X-axis represents distance along the path. You can move your cursor along the profile to examine elevation and distance at different locations.
If the elevation profile shows zero or does not display correctly, Google recommends checking that the Terrain layer is enabled.
Step 3: Find the Elevation Difference
Before calculating the elevation difference, you can learn How to Find Elevation on Google Earth to identify the elevation of your starting and ending points.
Identify the elevation at the beginning and end of the section.
For example:
- Starting elevation = 1,120 m
- Ending elevation = 1,150 m
The elevation difference is:
1,150 − 1,120 = 30 m
So, the terrain rises by 30 metres between the two points.
For a descending section, you can express the change as a negative value or report the magnitude separately and describe the direction as downhill.
Step 4: Find the Horizontal Distance
Next, determine the horizontal distance between the two locations.
Suppose the horizontal distance is:
300 m
You can then calculate the slope using:
Slope (%) = (30 ÷ 300) × 100
Slope = 10%
Therefore, the terrain has an approximate 10% slope over this section.
Example Calculation
Consider a proposed access road with:
| Measurement | Value |
|---|---|
| Starting elevation | 1,120 m |
| Ending elevation | 1,150 m |
| Elevation difference | 30 m |
| Horizontal distance | 300 m |
| Slope | 10% |
The same method can be applied to roads, drainage routes, pipelines, agricultural land, building sites, and other preliminary terrain assessments.
Can Google Earth Pro Calculate Slope Directly?
The elevation profile is particularly useful because it lets you examine slope, elevation, and distance along a path. However, for a simple overall slope between two points, you can calculate it yourself using the elevation difference and horizontal distance.
This approach is also useful when you want to calculate slope for only a particular section of a longer path. Google Earth Pro allows you to inspect portions of the elevation profile by selecting part of the path.
Important Accuracy Limitations
Google Earth Pro provides useful terrain information, but its measurements should not automatically be treated as survey-grade data.
Terrain models and imagery have limitations, and the result can vary depending on the quality and resolution of the underlying elevation data. A small difference in elevation can also produce a significant change in calculated slope when the horizontal distance is short.
For detailed engineering design, construction setting-out, legal boundary work, or other applications requiring high accuracy, use appropriate professional surveying equipment and verified topographic data.
It is also important to distinguish horizontal distance from the actual distance measured along a sloping surface. Using the wrong distance in the formula can produce a different result.
Conclusion
You can calculate slope using Google Earth Pro by creating a path, opening its elevation profile, determining the elevation difference and horizontal distance, and applying the percentage-slope formula.
The basic calculation is:
Slope (%) = (Elevation Difference ÷ Horizontal Distance) × 100
For preliminary site analysis and terrain assessment, this can be a convenient way to understand how quickly the ground rises or falls. For engineering or construction decisions requiring precise elevations, however, verify the results using reliable survey data.
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