Learn English – Do we use ‘work in’ or ‘at’ a gas station

Usually a letter my be from: 1. a person; 2. a company, hospital, etc.; 3. a specific place (from London; Germany; etc.) and to 1. a person; 2. an isnstitution (financial, economic, etc.). I received a latter from the Pope. denotes that I was the addressee, whereas I received a letter by the Pope. suggests that I am not a person the Pope wrote to.

All four of your options are grammatically correct. They just have slightly different connotations.

"The" is a definite article so generally indicates you are talking about a particular / specific instance of the noun. So "price of oil" denotes the price of the commodity in a generic, global sense, whereas "price of the oil" denotes the price of the specific container or quantity of oil - the context should make it clear which instance. Likewise "price of land" is talking about land in the abstract sense, "price of the land" is a particular plot which should be evident from context.

In your "shape of" examples we encounter another nuance of English which is that without any prior context as to what 'the' land in question is, there is a prospect to interpret land as a somewhat metaphorical synonym for country or nation. "The shape of land" makes me assume you will be writing about geology - the actual shape of physical ground. But the title "The shape of the land" makes me think this article could be about the sociocultural contours of the nation (so, as a Brit, the UK, but the reader may substitute their own of course).

"(The) Shape of Lands" meanwhile emphasises that there is more than one land, but does not (to my ear) clearly resolve this ambiguity. It could be about differing geologies, or a comparison of nations. I would probably lean more to assuming the former, because it is getting quite tenuous for the latter, but it's not impossible.

Of course here I am speaking about the without-context scenario. Assuming the title appeared in, say, Geology Monthly Magazine, this would likely be a non-issue.