For mapping in difficult terrain, you have options to facilitate path planning (see our Flight planning tools article). Overall, you will want to enable terrain following in difficult terrain.
The terrain data within WingtraPilot does not account for forest or other obstacles like buildings. If you want to map a forest or buildings, make sure to set the ground clearance to an appropriate value (we recommend normally the height of the tallest building + 20m). Since the mapped objects lie higher than the ground used in planning, effective GSD is typically better (lower) and overlaps are worse (lower) than planned. Therefore it is recommended to map forests and populated areas with higher overlaps. To enhance stitching robustness for such use cases, it is furthermore recommended not to fly very low (use slightly higher GSD than elsewhere).