Why Google Earth™? Why not?

One of our marketing guys showed me an email the other day asking him why everything isn’t being done in Google Earth™ (GE) these days, instead of all our expensive GIS software. Well, why not? It’s definitely one of the coolest things I’ve ever wasted an internet packet on. Like most of you, I’m a map nerd. I have piles of maps from old trips, maps on the walls, atlases, etc. GE lets me do that online. If I hear about someplace in the news, I can find it. If I want to look at random people’s photos of random places, I can do it. If I get bored at work—well, never mind…

Google Earth, with its availability of imagery of everywhere across broadband internet connections has made map nerds of everyone, from housewives to managers, while the participatory aspect embodied by mashups has established whole new applications and users of geospatial information.

So, why not use it for everything? Why do we still buy expensive GIS and photogrammetric systems? Every tool has its intended purpose; in this case the tool also includes the associated data resources. To determine suitability we need to understand both the tool and its included datasets.

The way to think of GE is as a map, more along the lines of a “you are here” map, more representational than metric. The imagery background, with its color and detail, gives a very authoritative impression. However, there are no guarantees on how accurate the imagery is and no consistent way to obtain the metadata for any particular image. Is it uncorrected, approximately rectified, or precisely orthorectified to make it the equivalent of a map? Is it from a satellite or from aerial sensors? When was it acquired? In terms of pure representation it doesn’t matter; in terms of metric accuracy, if you don’t know the characteristics of the imagery, it’s unusable.

Another issue is the unevenness of image coverage. Many parts of the world are covered with recent sub-meter color imagery, while others are not. Our family farm in eastern Kentucky, for example, has only 5-meter imagery. That may be for security reasons, although I doubt it.
The inclusion of additional data layers, especially mashups of several layers, can add to the uncertainty. Again, there’s usually no way to determine the metadata of the additional layers.

There are absolutely no guarantees of availability: for what types of data is available at any location, that the service will be accessible at any given time, or that Google will continue to provide GE under current terms and conditions. It’s unlikely that they’ll change a spectacularly successful business model, but nothing is certain on the Internet.

The main thing that makes GE a representational tool is that it has no analysis or processing capabilities, with the exception of SketchUp for constructing 3D building models. One of the factors driving the number of importers is that data must be produced and processed in external tools. Processing operations, such as resampling or reprojection, or GIS analyses such as proximity or intersection, must be done in external tools and the results exported into GE.

GE is optimized for distribution of processed information. There’s no supporting structure, such as a geodatabase, to maintain and select current data according to user requirements. KML files can be passed from user to user, but there is no version control or selection mechanism to maintain consistency among users. Note that while the GE enterprise version supports the distribution of enterprise data across an organization and to its customers, it again assumes that any processing and preparation occurs before data is loaded.

Please don’t take this as criticism of Google or Google Earth. As I said, I love it. It has introduced a huge community to geospatial concepts and imagery (I recently heard Michael Jones, CTO of GE, say that GE users are the ninth largest country in the world). We must be careful, however, that users understand the characteristics of the data and implications of those characteristics.

For more information, see http://earth.google.com.
An interesting article on the technology behind GE is at
http://www.realityprime.com/articles/how-google-earth-really-works

This article was originally published in the ASPRS Potomac Region newsletter (http://www.asprspotomac.org/).