Paris Metro/RER map

I'm also in the planning stages of my trip to Paris in 3 weeks and have found the website www.vianavigo.com very helpful for planning metro/RER trips, you can enter origin and destination and it will take you step by step and also includes buses. There's also an app which I will download for the trip.

Similar to London, if the crossing point is a white circle or two linked white circles, there is an interchange. If the lines on the map simply pass over each other, there is no station there and no interchange.

Mike, have a look at thus very helpful website:

parisbytrain.com

Also look at www.ratp.fr/en. One thing to note is that the junction between lines can involved a bit of a walk, especially when the names of the stations that are connected to each other are different. For example, you can connect to La Chapelle from Gare du Nord using a tunnel that is roughly 350 meters long. My friend claims it's 1/2 a kilometer but I think that is an exaggeration.

Mike, the official métro map is here: http://www.ratp.fr/informer/pdf/orienter/f_plan.php?fm=pdf&loc=reseaux&nompdf=metro
It marks all stations.

As Philip says, if there is a station marked (white circle and station name) you can change, and you will not have to use another ticket. This is most of the cases.
The RER lines (A, B, C, D, E) are limited stop, and often cross normal métro lines without stopping. This is shown on the map.

Thanks everyone. Norma and Chris, these ARE great maps--thank you!