The first thing to understand about this image is that it is not a single image. You're probably familiar with the practice of photo stitching -- panorama creation. This process combines multiple images to create a seamless, single finished image.
This image began life as 36 14.6-megapixel images. If the images did not overlap in anyway, that would be a 525-megapixel finished product. Now, the images do and must overlap. Lenses have color drop-off and vignetting on the edges, so there's a limited, central range where each image can contribute to the overall composition without causing strange lighting problems in a photo. So this image's original is actually 7,447 by 6,633 pixels -- 49.4 megapixels. Yes, your math is correct -- less than 10% (on average) of each image is used in the final composition.
Why, though, this amount of waste? The most in-focus part of an image is the center. As the image progresses to the edge of the image circle (and frame), the image quality begins to blur and darken. So using only the central portions of the photos means that only the best parts of the images are retained -- only the most-in-focus areas used.
You'll notice this image seems exceedingly sharp and detailed. Part of that is because only the sharpest part of each image is used and part of that is because this 49-megapixel image was downsampled to a 0.8-megapixel image for this post. The actual pixel-by-pixel clarity is not any greater than in a typical image.
The Internet contains myriad guides to photo stitching. Suffice to say, you will need a camera and a software capable of creating stitched images. There are purpose-made programs for this use if you don't have Photoshop.
For the other posts this week, we'll look at some of the pitfalls to this technique and why they occur.
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