More often then not, when you are building your base there will be some part of the terrain that you have either flattened or sheared edges, leaving you with an undisirable look to the surroundings. I have spent time to work with the majority of terrains that exist in Xenominer, in order to make this guide. But to warn you, terraforming can be just as time consuming as building your base.
I am not responsible for any undesired results!Edit
Since the most new players will decide to put their home within one of the first Craters they begin in, I will start here.
Flattening the Regolith!
First step of terraforming after finding a suitible base in this biome is to flatten the Regolith. This is easy. First, decide how low you want the base level of you base to be. Then, mine out a border to the area you are flattening, we will fix the sheared edges later. Next, you can either choose to start at the top or you can start at the bottom, as long as you mine it out in straight lines or chunks instead of randomly mining. While flattening you will want to make sure the base level is all Regolith, replacing any Basalt or ores you come across.
Eroding the walls...
Once you have your base flattened we can get to work on any shear edges that are left. Any craters that are apart of the border you made can be helpful when it comes down to eroding the walls. You want to start with small sections of wall at a time, digging each layer as a slope so the lowest is the farthest out, while the highest is the farthest in. While eroding the walls, you want to make sure and vary how far the bottem layer comes out, otherwise you will end up with a straight hill, unless you want that. Varying the layers will give the walls more depth and allow you to curve the walls, eventually making the area you flattened larger then it originally was. make sure to blend it in with any craters that are attached to it. If you can find out how to make the hills a couple blocks steep and still look nice, go for it.
Moving on in...
Once you have finally gotten the desired look of your crater you can start building your base, or if you already have built your base enjoy the view. You will probably have a lot more Regolith and Basalt then you know what to do with, you can throw that in your disposal area if you already have a large supply stored.
Some players may choose to build underground to completely avoid the radiation during the day. But be warry of the Venators you may have to evict from their Nests!
Choosing your cave.
Unless you plan on just digging out large box rooms in the Basalt, you'll want to find a cave system that fits your needs. If you want to build tall bases or towers, I recommend finding a shaft. If you plan on setting up an underground mining post the best choice would be above a lava tube, just high enough so you can get surface ores without much trouble aswell as the valuables found in the lava tubes.