Custom maps should be kept in a sub-directory of your EverQuest map directory. For example,

C:\users\public\Everquest\maps\Brewall's Maps
C:\users\public\Everquest\maps\Good's Maps

In-game, you switch between map folders via a dropdown in the top left corner of the map.

Brewall's maps are posted on their site, http://www.eqmaps.info
To get an idea of the care Brewall puts into mapping, look at the Map Comparisons here:
http://www.eqmaps.info/map-comparisons/

The map key is kept up-to-date here:
http://www.eqmaps.info/eq-map-files/mapping-standards/

• Brewall's map pack