The home area is the region of the map where your colonists can clean, extinguish fires, and make repairs. The home area is automatically expanded as colony structures are built. This is a setting that may be toggled by clicking the house icon directly above the Overview button. The home area is designated in dark blue when choosing to modify it.
Adding home area
To add others parts of the map to your home area click the Architect button in bottom left corner, then click Zone/Area and click Expand home area.
Now you can mark cells as home area by dragging the mouse. This is useful when you need your colonists to engage in a behavior like firefighting near your structures.
Removing home area
If you want to remove parts of the home area, go to Architect - Zone/Area and click Clear home area.
As when adding, drag the mouse to remove sections of the home area.