not surveyed or mapped

Not chartered; not supplied with a charter.

In an unchartable way.

Not chartable; that cannot be charted.

An area of sea that has not been surveyed, or whose details have not been entered on nautical charts. / (figuratively, in the plural) Any unknown and potentially dangerous situation.

plural of uncharted water

an area of land that has not been surveyed / Synonym of uncharted water (an unknown situation)

plural of uncharted territory

The quality of being uncharted.