I am a bit lost even to find the shortest safe way to the nearest city. How do you choose your routes for long journeys? Do you need to do compromises very often or change plans?
In the US I bought bicycle touring specific maps from Adventure Cycling Association. They're on the expensive side (I just paid about $50 for ~1,000 miles worth of maps), but I like knowing that someone has personally tested each route by bike and that food stops, bike shops and that sort of thing are marked.
I've met plenty of tourists who used GPS, road maps, or no maps at all, so in the end it really comes down to what your comfort level is.
There's a variety of touring styles to consider. There are people who plot every single metre of the journey and then there are people who just ride until they run out of time or money. I assume there are people who do whatever seems interesting on the day or who just obey whatever directions they get from whoever they meet. I've kinda done all of those.
In outback Australia direction-finding is often very easy: there's one road, you follow it. After a few hundred kilometres you might reach a T intersection and have to make a decision (at Newman in WA, for instance). At the other extreme is navigating the old medieval parts of European cities where there's a maze of little corridor-sized streets.
My preference is to plan a route based on roughly 50km a day through an area with a reasonable density of interesting things. So if I fly into Christchurch, NZ (don't do that right now, ok) with a month to spend I might plan on riding down through Tekapo, out to the coast at Moeraki then back, for a nominal distance of about 1000km (30km/day). But when I actually ride I expect to find diversions - ride up to the Hermitage (Aoraki), through the Otago Rail Trail, and so on, probably riding more like 1500-2000km. My goal is that if I see a sign saying "historic dam 5km" I can ride up to see what that is. Or if someone says "you have to see the eccentric monolith" I can ride that way. It's a balance between planning and aimless wandering that suits me.
For CANC2 we spent a couple of months planning out where we'd ride, how long it will take (roughly) for each stage and what food and so on we'd need posted to each drop point. We also started contacting communities along the way to set up media and school visits, but that's pretty much what you expect for a political ride. I've never done a solo or friend-group ride with that level of planning.
The intense planning usually means looking not just at distance, but conditions - gradients, expected weather, road conditions and so on. Read tour reports from other people, look at nearby tourist attractions (for whatever type of tourist you are), work out where you want to stop each day. Often you start with the list of attractions and work from there. Friends of mine who've done that often start with an event (like PBP, SPEZI) or some other reason to travel, then work out how long they can afford to tour for and buy air tickets accordingly.