It's a great idea - as long as you're wanting to go to places that don't exist, or willing to take roads that don't exist to places that are no longer there.* :)
Google maps is massively inaccurate and can be heavy on data. You're far better off using an offline mapping service based on OpenMaps. Currently Organic Maps is my mapping app of choice. It's updated every month, and is often based on local government information. The level of detail is amazing - down to post boxes, benches, drinking fountains, even (in our village) traffic bollards. There's also a function to find the nearest public toilet.
Just download the app and the map for the department you're going to be in, and you're away. No need for data, just update the map once a month if you want the absolute latest. I occasionally use Google maps for road closures, but that's it.
*Google has been convinced for 12 years there's a business called Fitzipark in our village. There isn't, there never has been, and despite being told by multiple people multiple times, haven't removed it. And most of the businesses in town are shown in the wrong place.