Google Earth combines data from a variety of sources that differ in their origins, resolution, age, and geometric accuracy. The objective is to create a visually pleasing picture of the Earth's surface. At a support for professional use is not thought of. Depending on the accuracy of how the elevation data of the mainland were determined. And that can be very different and is only very tedious or not researchable. Therefore, a general accuracy level can not be specified on Google Earth.
Here some examples:
The mountain Ještěd (Czech Republic). I know the height of the parking lot at the TV tower. It is 1012 m. Display of GE is 980 m. Further see table.
The altitude errors of the satellite systems Shuttle Radar Topography Mission (SRTM) Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) are given as 6 m. GE is already sufficiently accurate for private use. Whether this is sufficient for a professional use I can not say. Maybe, if you have one or more reference points?
An elevation profile (such as the course of a mountain stream) can be done quite well with GE. Also goes for hiking trails. For example:
Open Google Earth and view the desired region on your screen. 1. Click on "Add" in the menu bar and then on "Path". 2. Now use the mouse to mark your path on the map. You can either set individual waypoints by briefly pressing the left mouse button, or hold down the left mouse button while drawing the path. 3. Enter a name for the new path and confirm with "OK". The path now appears in the left pane of the program window under "My Places". 4. Click the path there with the right mouse button and select "Show elevation profile" in the context menu. Google Earth will then show the contour line on the map and below that the elevation profile. 5. You can see the minimum, average, and maximum elevation of the graph and see the exact distance, altitude difference, maximum grade, and average grade. If you move the mouse pointer over the elevation profile, Google Earth will show you the exact location with the respective values on the map.
Thanks willi1. Very descriptive explanation. In fact my work is to identify catchment boundaries for drainage design for a Highway (Culvert and Bridges design) and is a professional work. Have seen some people use this for the same purpose but I have my own doubts about the accuracy if use how to express the accuracy.
Seems like it is not suitable for professional works.