Here's a link to a NY Times article published today on Google's off line map app. Right now available for Android smart phones and projected for iOS by year end.
I tried that current option to download/save over wifi last year and it didn't really work. I picked up maps.me and had all the offline features in it. It worked great while we were in Italy, Switzerland and Germany in September.
Rick Steves book recommended citymaps2go - we used it all over Italy last month and it worked great. You have to download here at home, but once downloaded - we were able to use in Venice, Rome, Florence, Sorrento, etc with ease without using cellular data.
Because I was familiar with Google maps I used them primarily when I was in Europe a few weeks ago. I had to find directions from a Wi-Fi connection, take a screen shot...then the screen shot worked for me (I don't know how!). I would just pull it up and start walking in the direction with the arrow following me. If I needed to get to the next place I would duck into a Wi-Fi restaurant, get a coffee and plan our next course (find, screenshot). I have Citymaps2Go but was not familiar enough with it to use in Europe. I suggest you play around with the app in your home town to get to know it before using in a foreign place.