I use Google Earth Pro (7.1) on a daily basis to assess the acreage of US agricultural fields using the GE ruler.
What is the accuracy we can expect from Google Earth Pro for surface calculation? (the fields don't always have simple shapes and are sometimes in remote areas)
I found a few threads that partially cover this topic. But I didn't find any clear answer.
Best Answer
I think that might be because there is no single, clear answer. I'll try to summarize my knowledge and the two most related questions:
Let's start by taking Google Earth and even GIS out of the equation and only consider how accurate a measurement on an image can be. If the resolution of an image is a pixel is 1m, and you are zoomed in far enough to see individual pixels (original, not resampled for display purposes), you can measure to within +/- 1m. Now let's get that into GIS, which requires both orthorectification and georeferencing. Both can introduce error. On top of which, you're looking at errors introduced by (re)projection.
Now let's put that all into Google Earth, which is providing you a seamless interface to multiple original sources. All of which may vary in their original resolution and quality of the above processes, so right off there is no single accuracy measurement. This is why Google has that disclaimer about accuracy:
Source, as linked in question 2 above.
All of that is just for the accuracy of the imagery you're measuring from. Then add in the user interface - how far out are you zoomed when you do your measurements? Far enough in to see those individual original pixels, if they're even available to you? Or out far enough to see the entire field, or the field and its surroundings? What display resolution is your computer running, and how accurate/precise is your hand with the cursor as you mark the boundary? What distortions are introduced by the projection(s) Google Earth uses, which may change depending on where you are looking. The best you can do is find something of known distance near your feature and see what it measures at to estimate the error in that area.
So the short answer is, it varies.