A site plan generally starts with a survey, overlays the setbacks, may have topographic info, may discuss things like soil/erosion control, and ultimately will overlay the new square footage you plan to add, to scale and where you plan to build it.

It was certainly arid there, with no rain and not like the typical volcanic islands which are more tropical and have hills, soil and rain forests.

GIS maps are typically off you need to get wetlands flagged by a soil scientist. 

Most of the clothes will have some soiling on them for growth to be viable.  

Expansive clay soils  exteme heat and temp swings and big rains...

Although I have no first hand experience in this, it has been reported here on BP that Dallas homes are very prone to foundation problems because of the underlying soil. 

Including myself, there are only two of us agents underneath him.

.), is the lot infill, do you need to re-zone, are water/sewer available (if not, get a soil scientist to test the soils), impact/tap fees, etc. 

But to a GC, maybe it's not as scary underneath all of it?

some pools are sinking, breaking away from their coving, empty spots underneath, cracks…you name it.