There are many elements the go into making the wonderful scenery that you see in MSFS2002. Auto-generated and custom 3D objects, land use textures and rendering effects such as shadows and reflection all work together to create a convincing scene. The foundation for all that is the actual 3D land surface on which everything else is built. Without a solid and accurate foundation, all the rest is just fancy window dressing. This article will take a close look at the details, benefits and cost of using accurate topographical data in MSFS2002
The shape of the landscape that you see out the cockpit window is a digital representation of the real world. The form of the landscape is determined by the height of thousands of individual data points, each representing a single elevation on the earth's surface. It's the lateral spacing and the quality of the original data that determines just how closely the 3D shape created from these points mimics the real world. The following illustrations show how the accuracy of this representation changes as the horizontal resolution (spacing) is reduced.
Above is an 1800 meter long
imaginary slice through the earth's surface. Maximum vertical relief is 350
meters. The small canyon on the right is approximately 150 meters wide and 45
meters deep. 
Here is the same scene as it
would be represented by a horizontal resolution of 19.1 meters. It's easy to
see that at this scale, the shape of the landscape is preserved very
accurately.
At 38.2 meters you can start to see some loss of
fine detail but the basic character of the landscape is preserved very well.
It's interesting to note that this is the resolution that's used for the
bulk of Denny's Real Scene and most other mesh upgrade packages.
At 76.4 meters we're really starting to pay a
price. While the overall "twin peaks" are still recognizable, the small
canyon on the right has lost most of it's definition while the bowl like
valley on the left is becoming v shaped.
At 152.9 meters the degradation continues. The
overall shapes of the major peaks are becoming unrecognizable and small
features are lost completely.
Now, at 305.8 meters most resemblance to the
original scenery is gone. Keep in mind that if we were looking at a larger
slice, say 9000 meters wide, the effects of decreasing the resolution to
this level would be less noticeable. Still, you can easily see the basic
effect. As resolution is decreased the basic shape and character of the
landscape is gradually lost to the point where things are no longer
recognizable. Where this point is in terms of horizontal resolution depends
very much on both the nature of the topography and the size of its major
features. A small steep-sided canyon will be effected to a higher degree then a
large mountain. A highly detailed feature like the Grand Canyon with a lot
of fast changing vertical relief will be much more effected then say, the
rolling hills of Vermont.