Above/over

Hanuman,

I'm sorry to say that your question is too broad to handle in a forum post. My dictionary shows 12 definitions of "above" and 34 for "over"!

If we limit our discussion to just the prepositional uses where "above" or "over" are spatial concepts, the two are extremely similar. One of the definitions of "above" in my dictionary contains the word "over"; one of the definitions of "over" contains the word "above"!

There was a large lamp above the table.
There was a large lamp over the table.

Suddenly we saw a flying saucer above the house.
Suddenly we saw a flying saucer over the house.

When conditions are right, fog forms above the lake.
When conditions are right, fog forms over the lake.

The sign was visible above the door.
The sign was visible over the door.

"X is above Y" is the most neutral way to express the relationship. X and Y have equal status in this structure. "X is over Y" is very slightly different, giving slightly more prominence to X, making us feel that X is somehow bigger or more voluminous or closer to Y. Other than these vague feelings, we'll need to see if others post more elucidating information on it.

When motion is implied, "above" may give more of a feeling that the motion is not goal-oriented; "over" may give more of a feeling that a definite trajectory is involved.

The plane flew above the city. The plane flew in circles above the city.
The plane flew over the city. The plane flew over the city on its way to Chicago.

This effect is more obvious in the following sentences, the first of which is rather difficult to contextualize, almost to the point of meaninglessness.

We jumped above the wall. (We were doing jumping in a place which was higher than the wall. Or, alternately, we jumped to a position which was above the wall.)
We jumped over the wall. (We started on one side of the wall and jumped so as to end up on the other side of the wall.)

CJ