Oregon 6xx lets you have multiple custom maps on sd card (x:\Garmin\CustomMaps\)
and/or in memory and turn on just one custom map or any combo or all custom maps. All custom maps together can have up to 500 tiles 1024 x 1024 images. On 62 all of the custom maps on the sd card and in memory are either all on or all off. The limit on 62 is a total of 100 tiles.
Spoiler: guidelines to remember when creating Garmin Custom Maps