Spoiler: PC InstallerMapData_USA-1.zip 1.04 GB:
MapData_USA-2.zip 786.7 MB:
MapData_USA-3.zip 685.4 MB:
MapData_USA-4.zip 2.5 MB:
OpenStreetMap_USA.exe 245 KB:
Download all parts to the same folder and execute the last one; this will install in PC and you will be able to see and handle the map in Basecamp. No need to uncompress anything.