Flight path not showing up when no basemap is available

With no points of reference doing a flight layout doesn’t make much sense anyway. If you want to have a custom path previously defined, you can do so using the methods discussed in the previous answers from today’s questions. The best way to make sure you have a base map to operate off-line is to view the general area that you will be operating in while you are still on Internet and pack up the base map information for that mission at that time. we do not plan for people flying with no basemap information.

With no points of reference doing a flight layout doesn’t make much sense anyway.

Yep, it is hard to make a flight layout that way, but you have no choice when you are offgrid for weeks at the time in a territory spanning several thousands square kilometers. Currently, I'm guessing my flight plan by using the width/height measurement of the flight layout displayed in Map Pilot Pro relative to my current position. This is the only option because basemap caching before going offgrid cannot be big enough (in Map Pilot Pro and with current storage limit). Hovewer, I can have a computer with me containing all the data I might ever need and only transfert to my phone what I truly need when I'll know what I need to map. I'm doing mapping for research purpose in forest after huge wildfires, it's only when I have my feet in the forest that I'll know what needs to be mapped.

If you really don't plan to ever offer an offline import of custom basemap, a default low resolution (30m) global hillshade could be included. The user might have to pre-download a territory (the Americas, Asia/Europe, Australia, Africa, for example, or a custom selection allowing for several thousand square kilometers). That would be of some help... but I doubt that it is less work than making Map Pilot Pro able to read geotiff files. In all cases, I know this not trivial to implement (I mainly do programming for a living, just not in Swift or Kotlin). Thanks for your current app, I just wish it could do a little bit more.

Caching data sources for offline viewing is complicated since most of the data has different licensing requirements.

A typical GeoTiff for a decent size area is at least hundreds of MB, if not bigger. That is still a file size that is not handled well on mobile devices. That is why you don't see other apps doing it. Yes, it is something that could be done but is of little utility to most users. 

If you have all that data on a computer with you I would recommend making a KML flight boundary or flight path and using that to collect your data. 

You have to realize that what you are trying to do is not something 99.9999% of users are trying to do so throwing a ton of engineering money at it isn't going to help most users. We don't tend to add features that only benefit a couple of people while complicating the interface for others. If you want to fund the addition of these features we can certain provide you with a quote.