Because dynamically created maps do not have a title, you should describe the map in square brackets and also include a retrieval date because the page could change over time.
Example
Reference List:
Google. (n.d.). [Google Maps directions for driving from Ingolstadt, Germany, to Geneva, Switzerland]. Retrieved August 4, 2015, from https://goo.gl/maps/ILt8
Parenthetical citations: (Google, n.d.)
Narrative citations: Google (n.d.)
