The Apple MAPS app has the ability to download maps for use in areas when no cellular service is available, slow or expensive . Your iPhone GPS can then navigate within the downloaded areas. Google Maps and many other map apps have the same download feature. I use a paid app called Pocket Earth Pro that has features I enjoy and I can select downloaded maps by city, state, country, etc. for future use. Prior to a trip I usually load all the regions or countries I will visit. I then have quick and accurate maps with my location available instantly without needing to get cellular service.