Creating a new base map

That is certainly the catch 22 of using imagery for mission planning. 

You can manually fly and collect coordinates to use as your survey area and go from there. 

or

You can import a KML that was created using some information from somewhere else to use as a guideline.

or

You can import 3rd party basemap data. 

or

You can guess!

Usually Apple Maps (which is what is actually used as the default basemap) will have enough information to at least give you some general context to get started.