The "fuzzy zone" is an attribute of several nodes. As an example the Surface Layer node and the Distribution Shader use a fuzzy zone for altitude and slope constraints. The fuzzy zone is basically a way of blending smoothly from full coverage to no coverage.
As an example consider a maximum altitude constraint of 1000 for a Surface Layer node. None of the surface layer will appear above 1000m. Below 1000m more and more of the surface layer will be shown. Close to 1000m the layer will be very transparent and it will get more opaque the lower it goes.
The fuzzy zone parameter is not entirely straightforward. It's used to control the curve used for blending. As a rough guide with altitude constraints the surface layer will be opaque at about 5 times the fuzzy zone setting. For example the default fuzzy zone is 200 and 200 times 5 is 1000. This means that the surface will be fully opaque at an altitude 1000m below the maximum altitude constraint, which would be an altitude of 0 in this case.
That might seem a lot but the curve used for blending is a special shape. Have a look at the graph below. This graph shows the curve used for blending the fuzzy zone. The X axis along the bottom shows distance in metres. The Y axis, running vertically, shows the amount of transparency/opacity of the blending. 0 at the bottom means fully transparent and 1, at the top, means completely opaque.
The red curve corresponds to a fuzzy zone setting of 200. As you can see the curve climbs fairly steeply to begin with. This means that opacity is increasing. At about 460m the layer has reached 0.9 or 90% opacity. After that stage the opacity increases more slowly until around 1000m it has reached a little over 0.99 or 99%. Technically the layer never reaches exactly 100% opacity but it's near enough for practical purposes.
To put it in technical terms the fuzzy zone parameter corresponds to the point on the curve where opacity is 0.63. An easier way to think of it is that the fuzzy zone parameter controls how quickly the layer becomes opaque. A smaller value will make it happen more quickly. On the graph the blue curve corresponds to a fuzzy zone value of 50. As you can see the curve is much steeper initially and flattens off more quickly. Using the "times 5" rule of thumb we can say that the layer reaches full opacity at about 250m - 5 times 50 is 250.
If you wanted the surface layer to go all the way to 1000m without blending you can set the fuzzy zone parameter to 0.
More detailed information about the fuzzy zone and slope constraints will follow but the fuzzy zone behaviour is essentially the same as with altitude constraints.
A single object or device in the node network which generates or modifies data and may accept input data or create output data or both, depending on its function. Nodes usually have their own settings which control the data they create or how they modify data passing through them. Nodes are connected together in a network to perform work in a network-based user interface. In Terragen 2 nodes are connected together to describe a scene.
A parameter is an individual setting in a node parameter view which controls some aspect of the node.