This is based only on my personal experience. After having my own issues with downloading and storing off-line maps, I searched for any documentation from DJI and couldn't find it.
There seems to be a maximum size, in terms of megabytes, for each map tile you download. When I chose a rural area, with little detail, I was able to download a rather large area (a good chunk of northwest Virginia in my case). When I chose a metropolitan area, with a multitude of streets and other details, the area I could draw the square around (and therefore download) was much smaller. I couldn't find a way to determine the file size for each map tile, but my impression was that each one is limited in terms of how much data it contains. For a rural area, you might be able to grab an entire state. For a city area, the maximum area is much smaller.
There's also an overall limit in terms of map data stored across all the map tiles you download. I was able to download and use eight separate map tiles (a combination of rural and metropolitan areas). When I tried downloading a ninth segment; when it got to 39% it stopped and displayed "You must delete some offline region and resume download", followed by a cryptic button that simply said "Yes" underneath. Some users have reported being able to download and use more than eight segments; others have been blocked at fewer than eight. Again, it seems to be file-size related. Or maybe this is related to which platform (iPhone vs. Android) you're using. Who knows?
Because the app started to download data and then stopped at 39%, it would seem the limit is somehow memory- or storage-space limited rather than limited to a fixed number of maps. If this is memory-limited, it could also mean that the app might allow more or fewer map segments depending on how much total information is included with the map segments you download. It would be nice if there were documentation on this.
After all this, I discovered that filling up the allocated off-line maps storage space might not be a good idea. When I took my Mavic Air to a location without a WiFi connection, but in the center of an area I had downloaded for off-line use, all I saw in the map area in the corner of the screen was an empty black rectangle. No matter what I did, I couldn't get the off-line map to display. I returned home, and on a hunch I deleted a few of the off-line maps I knew I wouldn't need for a few days. I went back to the same area (no WiFi but off-line map), and voila, the off-line map magically appeared.
One of two things had apparently happened: Either one of the maps I deleted was somehow corrupted and prevented any off-line maps from displaying, or completely filling up the space reserved for off-line maps somehow messed things up.
The solution(s) I found might or might not help you, but it couldn't hurt to try these two approaches:
- If you've maxed out the map storage and seen an error message that says you have to delete an existing map segment to free up space, delete a couple of the maps you've downloaded. I'm convinced the app gets flaky when the space reserved for map storage is maxed out (or nearly maxed out).
- Delete and re-download the map that wouldn't display, then try again. You might have somehow wound up with corrupted data that won't display.
Larry
P.S. To answer your first question
, if the off-line maps are working correctly, you shouldn't have to do anything to get them to display. When you fly outside of WiFi in an area where you've downloaded off-line maps, they'll simply show up in that box in the corner of the screen.
