One of the reasons for choosing an iPhone in the first place was to reduce the number of gadgets I needed to carry. Although we still use dedicated cameras for best picture quality, the iPhone has filled the gap for many other tools.
While the iPhone has a maps application, and some folks add the Google Maps App to their phone, both of these require a data connection to do trip planning. Google has recently updated their app to cache or download routes and maps, but I wanted more independence, especially for traveling internationally. I settled on a European product Copilot, which through the purchase of additional maps provides most of the functionality of a stand-alone GPS from the usual suppliers. On a recent trip through parts of Europe, I found it's route planning superior to that installed in the Volvo we had rented. There were a few locations we had to find a physical address, and for two we used the posted latitude and longitude from a tourism document, but most locations were available through the existing points of interest in the maps database. We found it valuable to have the maps pre-loaded, as we could easily do route planning without needing an internet connection.
We found this product well worth the $15 for purchase including USA and Canada maps. A small premium added those for the parts of Europe we toured.
You can learn more about Copilot on their website