So if Airport Lighting is selected from the drop down, you want Engineering displayed in an adjacent cell?
If so, that can be done by putting the category next to each subcategory (Engineering to the right of Airport lighting, etc.) and just do a vlookup.
You might want to consider, nested dropdowns in which case you would select one of the 5 categories (Housing, Gen'l Building, etc.) which would then populate another dropdown with the subcategories for that category.
You can read how to do that
here. I have attached an example using your data.