how do I install detailed topo map in basecamp?
Depends on which map you mean and whether the map maker supplies an 'install to computer' option so need more details to advise correctly.
An excellent source of auto-routing road and topo maps for Garmin is here and avoids the high cost of Garmin maps: https://alternativaslibres.org/en/index.php
This site is free but is well worth contributing towards. A friend wanted maps of an area in Peru and was stunned at the detail.
And numerous others are available, but no idea yet what the OP is trying to do.
