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ArmA 3 Terrain Builder, ArmA 3 Terrain Builder Support Forum

If you don't have satellite mask created by other tools like L3DT or perhaps made by yourself in image editor (Photoshop / GIMP), you can create basic satellite mask (surface mask) in terrain builder.

Create shapes according to vegetation, place forests etc stuff which require different mask type.

RMB shape layer and choose surface mask to be used with this layers shapes.

Then you can export satellite mask image with these surface colors. Use file → export -> shapes to imagery.