Segments - This spinner sets the number of segments to be generated in the X and Y directions. By using more segments, you can create a terrain with more detail, which is perfect for very high resolution landscapes. However, be aware that higher segments (over 1000) will slow the system down since more detail must be generated.
Displacement Map - Left-click on this button to open the Material/Map Browser window where you can choose any 3ds Max texture map that fits your needs. You can also drag and drop any map from the 3ds Max Material Editor to the Displacement map button and vice-versa. Please note that, as long as you do not have a grid generated, all changes to the Displacement map will be reflected on the viewport mesh.
Generate Grid - To be able to render a terrain or to apply any modifications (such as painting elevations or slopes), you will need to generate the Terrain first. Once the grid is generated, any changes to the Displacement map will be ignored.
Erase Grid - This button will erase the previously generated grid, and the viewport mesh will then use the Displacement map.
The Terra Editor will generate an empty grid if you start painting described next.