The following is taken from the ffxiv official website (not the lodestone):

A map is as precise
As the malms walked in her making,
Yet I fear these feet
Have but far too few between them

May she serve faithfully
Any who would employ her for good,
And shun all who would fill
Her borders with blood

Twelve see the steps taken
By those who heed her humble guidance
Ensure her legacy endures

Roddard Ironheart
Year 1506 of the 6th Astral Era

The vast realm of Eorzea, comprising the continent of Aldenard and its outlying islands, has seen the rise of a civlization with peoples as diverse as its environs. Throughout its history, the landscape has played home to a number of city–states–the tenuous relations among them fluctuating between friendly and hostile.

The pantheon of the Twelve is followed devoutly by most, and doctrine holds that the past wars of the realm were the wars of the heavens, with the gods and goddesses laying their favor with nations to champion them. In this way, war spread throughout the realm, discouraging unity and peace.

As a result, years passed without the lay of the land and its borders ever being mapped in their entirety. It was not until some 70 years ago, when an intrepid soul set out to wander the land, at great peril to himself, that the first map of Eorzea was completed.

Since then, the original rendering has been amended and improved by others, and the form it takes today is used by adventurers across the realm as an indispensable guide on their travels.
And that's how we got our map in lore terms. So the idea is that there is a map commercially available, or at least distributed by the adventurer's guild, that is considered to be indispensable for an adventurer.

I hope that helps add context for the in-game map (and also why it never seems to be 100% accurate).