Help With This Engineering Question

Usually hatching indicates the cross-sectional shape and material of a cut-away part. There are standard hatch patterns for steel, other metals, rubber, earth, concrete, etc.

In "key plans" a hatched area indicates what part of the overall building is being shown on the drawing sheet in question.

There are other miscellaneous uses of hatching, usually explained in a legend.

Could it be used to show hidden details also?

It depends as different hatching patterns mean different things, and even the same hatching pattern can mean something different depending on what drawing standard was used and industry the drawing was for.

Generally you can tell given the information located on the drawing along with looking at the associated drawings to discover the meaning.

As you have posted this in civil engineering (not really my area of expertise) I cannot really comment on, or give a list of, the different types of hatching patterns and what they could relate to.

Hatching is like a symbol or identification mark to differentiate the various or separate structural items.

Check the "Legends" sheet, "Drawing Notes", or "Specifications".

What I have found to be typical with electrical drawings is that hatching will indicate "NIC" items - not in contract (not in scope) or items to be demo'd.

If in doubt, submit an RFI (request for information) to the engineer that produced or signed off on the drawings.

In sectional engineering drawings, hatching indicate the solid portions of the object encountered by a particular section plane. Non hatched area are hollow portion. For example, for a piece of pipe if section plane is across the length, we get two parallel hatched areas in drawing. But if section plane is across its diameter, we get a circular hatched area identified by pipe ID and OD.