unity - Tools or techniques for UV unwrapping/texturing terrain with features such as roads?

I'm trying to create a map similar to Outset island in Loz: Wind Waker. Here is an example of what I'm trying to create:

As you can see, the roads more or less have dedicated tris. However, when I look at the UV data, it looks like a complete mess:

For reference, this is the texture without any overlays:

I have no idea how to go about creating a similar effect in my own game -- are there any tools I can use? What is this technique called?

Answer

It's UV-mapping. There are no rules to say it has to be neat, it is just preferred and encouraged by most to have a neat UV layout.

UV-mapping is about making a part of a texture show on a certain part of the mesh. We can use seams to help position parts of the layout neatly. In your example I don't think any seams have been used and probably no effort has been made to make a neat layout.

UV's use a repeating coordinate system, the layout that appears outside of the image will still use the same image, you will find the matching texture if you tile the image.

While we usually try to avoid stretching the layout, a simple texture can hide stretching, in this case, the patch of green at the top you can see has been repeated using different scales to get some variation.

At the end of the day, it is about the texture on the model looking good, not what the UV layout looks like.