  Google Earth is the most popular virtual globe in use today. Given its
popularity and usefulness, most users do not pay close attention to the
positional accuracy of the imagery, and there is limited information on the
subject. This study evaluates the horizontal accuracy of historical GE imagery
at four epochs between year 2000 and 2018, and the vertical accuracy of its
elevation data within Lagos State in Nigeria, West Africa. The horizontal
accuracies of the images were evaluated by comparison with a very high
resolution (VHR) digital orthophoto while the vertical accuracy was assessed by
comparison with a network of 558 ground control points. The GE elevations were
also compared to elevation data from two readily available 30m digital
elevation models (DEMs), the Shuttle Radar Topography Mission (SRTM) v3.0 and
the Advanced Land Observing Satellite World 3D (AW3D) DEM v2.1. The most recent
GE imagery (year 2018) was the most accurate while year 2000 was the least
accurate. This shows a continuous enhancement in the accuracy and reliability
of satellite imagery data sources which form the source of Google Earth data.
In terms of the vertical accuracy, GE elevation data had the highest RMSE of
6.213m followed by AW3D with an RMSE of 4.388m and SRTM with an RMSE of 3.682m.
Although the vertical accuracy of SRTM and AW3D are superior, Google Earth
still presents clear advantages in terms of its ease of use and contextual
awareness.
