Hyrule is the setting of The Legend of Zelda. The terrain of Hyrule varies according to different time periods. The timeline known as Hyrule's Decline or The Last Hero follows the events of The Sealing War, The Era of Light and Dark, The Gold Era, and The Era of Decline.
Changes in the landscape are possibly due to geological changes, a subjective landscape based on perspective and perception, a sort of reformatting of the landscape by magical forces, or a landscape that is abstracted in the in-game graphics and is not representative of the true landscape.
While the original game suggests a 1:1 scale between the map and the character, the idea of an abstraction of the landscape can be seen in Hyrule Warriors, where each screen of the original game represents a more detailed environment.
The map of The Adventure of Link is not on a 1:1 scale, as towns, palaces and monsters lead the hero to a more detailed side scrolling view, suggesting far more landscape than what the map is showing. The land is supposed to be Northern Hyrule, with the suggestion that the Death Mountain to the south shares the same mountain range as the Death Mountain to the north of the original map. Beyond this, there are not enough details to properly represent the position of Northern Hyrule relative to the original map.
The combined map of Hyrule and Northern Hyrule lacks a proper scale, as it is unclear how relative in size a Zelda I screen is compared to a Zelda II screen, and it is unclear what scale the monsters and hero of Zelda II represent comapred to Zelda I.
The features of Death Mountain in Zelda II are vague, appearing as a coastal mountain range with the ocean to the east. Is this coast the same coast as eastern side of the Zelda I map? Would the entire Zelda I map fit in the narrow range of mountains in Zelda II?
The bottom of the map may contain a mountain range that extends further to become the Death Mountain of Zelda I. It is also possible that the Zelda II map is not oriented in cardinal north, but is oriented in a different direction. Northern Hyrule may be to the Northeast or Northwest of Hyrule, rather than directly north.
There are many scenarios, though the exact details of the terrain remain vague.