Urborg doubt

[Thiagobones]

Hi,

I have a question about the Legendary land {Urborg, Tomb of Yawgmoth}.
So, it says every land is a swamp in addition to its type....
does that mean that every land generates its basic mana PLUS the black mana or it generates one OR another?

Thanks

[Raven316]

It generates one mana of either black or whatever the other land produces

[Thiagobones]

It generates one mana of either black or whatever the other land produces

Thanks!