SketchUp contains a powerful built-in tool designed for importing terrain, previously based on Google Earth’s terrain data. These days it’s based on Digital Elevation Model (DEM) data, giving you a perfect representation of the earth’s surface without any coverings like trees, buildings, or other objects sitting on the surface. This DEM data comes from a variety of reliable sources including high resolution Lidar, an incredibly accurate way to determine what’s what by targeting an object or a surface with a laser then measuring the time it takes the reflected light to come back to the receiver. Import data like this and you’ll always have a super-accurate picture of the real-life ground you’re designing on.