By default the Map appilications stores its files on the nonremoveable Internal Memory "card". This drive is unaffected when reflashing the OS. If you use the File Manager to navigate to Internal memory card > map you should see a folder for each map, plus some others. I have...

mapdata
mapdata_Canada-Alaska
mapdata_UK-Ireland
mapdata_USA West
navicore
versions

"mapdata" is the current active map, in my setup this is "USA East". Evidently the application simply renames folders when you switch maps.

"versions" appears to contain only a single text file.

"navicore" appears to store settings and multiple copies of legal notices and sound files in various languages. You could try moving the navicore folder to another drive (such as a removeable SD card or a PC) to test if Map will then run, but keep a copy of the original navicore folder.

My navicore folder contains 50 subfolders, 2051files, and uses 29.1 MB of storage. As a test I moved it to another drive and started Map. It automatically recreated the navicore folder, but with only 3 subfolders, 28 files and 410kb. Most of the difference is the sound files which were, of course, not automatically recreated.