The ‘Image Overlay’ tool is the key to an extremely simple, surprisingly powerful, and somehow little known trick in Google Earth. The tool allows anyone to copy maps out of print documents, drop them onto the terrain model in Google Earth, and then browse the maps in 3D – something that even the authors were often not able to do. It takes less than 5 minutes to import the maps in this way, and as it’s so easy, I often use it while reading scientific papers or reports in order to better understand the sites and context of the figures. In the example presented here, I refer to a useful paper from G.J. Hearn (2002)
summarizing the practical challenges of mapping and road engineering in some of the most difficult terrain in the world. The experience and insight conveyed in papers like this are very important for the future avoidance and mitigation of geohazards, a quality that becomes particularly apparent when reading the paper in association with 3D maps created using the Image Overlay tool.
The steps required to transfer a map from paper (or almost-paper) to a 3D relief are described below.
The .kmz maps for this example can be downloaded for Google Earth here
. As well as these being nice examples of geomorphological mapping for geotechnical applications, it’s interesting to compare the proposed roads to those now constructed (see the GE ‘Roads’ layer), and in particular see how both projects were directed by the results of the mapping investigations.
So, while this isn’t a difficult process, hopefully the comparison of the 2D map in the first image with the 3D representation above gives an idea how useful this technique can be. And as usual, (thanks to Google) this technique is free for everyone to use, provided the original publishers are wise enough to embrace the benefits of open access – but that’s another story!
Hearn, 2002, Engineering geomorphology for road design in unstable mountainous areas: lessons learnt after 25 years in Nepal. Quarterly Journal of Engineering Geology & Hydrogeology v. 35 no. 2 p. 143-154 doi: 10.1144/1470-9236/2000-56