Article - "a" or "the" or plural for countable nouns?

I think a countable noun are usually of the following 3 forms:

• the + countable noun (single form)


• a + countable noun (single form)


• countable noun (plural form)

I am confused about which to pick for the following sentence. Should it be

The map is usually a crucial prerequisite for location services.

OR

A map is usually a crucial prerequisite for location services.

OR

Maps are usually a crucial prerequisite for location services.

Answer

The definite article, the indefinite article and the zero article can all be used when a noun phrase makes generic reference, that is, when it refers to a whole class, rather than just one or more instances of the class. In some contexts, just one of the three is appropriate, but all three sentences in your example can, to adapt the words of the ‘Longman Student Grammar of Spoken and Written English’, be understood to express a general truth about the class of things called maps.

In the second part of each sentence, you need to change ‘for location services’ to ‘for the location of services’ or ‘for locating services’.