Earlier service Google Maps was able to pave only pedestrian or automobile routes through Paris. However, many guests of the French capital prefer to use public transport instead of cars for long movements in the city.
Hence, in the end of this autumn maps developers of Google added in this service the possibility to pave your route, including lines of the metro and RER trains (Réseau express régional d’Île-de-France).
Subway and regional trains supplement each other effectively (from 257 RER stations 33 are located in Paris); by the way, tickets for RER can be bought on metro stations. RER routes are very convenient, because they connect the capital and its suburbs.
Right now, advanced features of Parisian maps of Google affect the center of the city mainly. In near future developers plan to plug in calculation of routes for remote districts and suburbs of Paris, and, perhaps, to add the main lines of buses and trams.
Google Maps calculate (however, a little optimistically) the time you will spend for the way, taking into account not only its length, but also approximate intervals between trains.