Do I need to account for topography when planning a survey?

Short Answer: Yes, always account for elevation variations if it's greater than half the electrode spacing.

Long Answer: Yes, you must always account for topography (variations in elevation), but only if it is greater than half the electrode spacing. This is because you must input the exact location of each electrode or the inversion calculations will introduce positional error in the final solution.

You'll even need to make the terrain correction if you're just doing a 2D line.

If you have really uneven terrain close to the line in all directions—you will need to invert the data with terrain using the EarthImager3D™ inversion modeling software.