What happens to other land types (e.g. Legendary/Artifact) when some effects change the basic land types?

Question

Taking up a topic already addressed, for example, with the question:
What happens when two global enchantments affect the same type of permanent (e.g.lands),
with this question I would like to add a little and simple clarification to this kind of situations.

If a Legendary Land - such as Hammerheim - or an Artifact Land - as Vault of Whispers - is enchanted by cards like Evil Presence or Phantasmal Terrain, it becomes a basic land.

But what happens to its other types?

In other words the land, now transformed by one of the two enchant land above, as well as being now a basic land:

1. still maintains his original other type, that is, it is still legendary or still an artifact (as in the second example); or
2. no longer maintains any other types, but it is only a non-basic land.

Answer 1

It might be a bit confusing, but 'legendary' and 'artifact' are not land subtypes, like Swamp and Mountain are. 'Legendary' is a supertype, and 'artifact' is a type.

305.7. If an effect sets a land’s subtype to one or more of the basic land types, the land no longer has its old land type.

Evil Presence and Phantasmal Terrain do not remove 'legendary' and 'artifact', they influence the subtype. Hammerheim and Vault of Whispers don't have a subtype, but they will lose their abilities:

The enchanted land loses its existing land types and any abilities printed on it. It now has the land type Swamp and has the ability “Tap: Add Black.” Evil Presence doesn’t change the enchanted land’s name or whether it’s legendary, basic, or snow.

(from the rulings below Evil Presence)

So a Hammerheim enchanted with an Evil Presence will still be legendary but only able to tap for black mana; a Vault of Whispers enchanted with Phantasmal Terrain set to 'Mountain' will still be an artifact land but only be able to tap for red mana.

Answer 2

The Gatherer Link for Spreading Seas says

Spreading Seas {1}{U}

Enchantment — Aura

Enchant land

When Spreading Seas enters the battlefield, draw a card.

Enchanted land is an Island.

A ruling also adds:

The enchanted land loses its existing land types and any abilities printed on it. It now has the land type Island and has the ability to tap to add {U} to its controller’s mana pool. Spreading Seas doesn’t change the enchanted land’s name or whether it’s legendary, basic, or snow.

There are 3 components to the type line: the supertype, the type, and the subtype. The short answer is that the supertype (Legendary, Basic or not, or Snow) or type (artifact, enchantment, etc) rarely change. A card like Spreading Seas overwrites all subtypes and replaces them with 'Island', but it leaves supertypes and types alone. Spreading Seas doesn't eliminate supertypes like Legendary or types like artifact, or add any like Basic.

Spreading Seas makes a land an Island but it doesn't make it a basic land. Dark Depths enchanted by Spreading Seas is a Legendary Snow Island, but not a basic Island.

However, lands made into basic land types lose abilities. Blood Moon doesn't remove the artifact type from Darksteel Citadel (although it does lose Indestructible). So in the Dark Depths example, it will tap for U but not have any of the text about ice counters anymore. Any counters on the card remain, but they are nonfunctional as long as it is an Island.