Prismatic Geoscope

You can activate Prismatic Geoscope's mana ability if you have no basic land types among lands you control, but it won't produce any mana.

The colors of mana that Prismatic Geoscope can produce aren't related to the specific basic land types among lands you control. For example, if you control a Plains and an Island, you can activate Prismatic Geoscope's ability to add {R}{G}.

To determine the number of basic land types among lands you control, look for the Plains, Island, Swamp, Mountain, and Forest subtypes among the lands you control. Count each subtype that appears one or more times toward the number of basic land types among lands you control. This number can't exceed five.