GPSMAP 79sc problem with multiple maps installed

I have a GPSMAP 79SC It comes prepackaged with the bluechart g3 map. I just installed a free gmaptool topo map. I installed the base US Topo map with all 7 US regions combined. The topo map works fine. The problem is that I don't get the bluechart g3 detail anymore. It's looks like the device only handles one map (i.e. the last one installed). Is that how it works? Is there a way for me to disable the topo map on the device so that the bluechart map will show? Is there a way for me to make one of the installed maps have precedence over the other map in terms of displaying. I only need one or the other map displaying depending on whether I'm kayaking of forest foraging. I'd like both to be installed on the device since I've got plenty of storage space with the addition of a 32 GB SD card. Right now I just don't see a way I can accomplish this other than by deleting the topo map when I need the bluechart g3 map to display. But that means I need to reinstall the topo maps each time I needed to use them. Any thoughts on how to solve this problem would be greatly appreciated. It's also helpful to know whether what I'm trying to do is supposed to work or not! This device is replacing a Garmin Oregon 400, and I got both topo maps and bluechart maps both to work together.

 

I just learned that in the menu item "Setup/Map/Configure Maps" you can select a map and disable it from displaying. It's a very course level for controlling the display of maps, but it does solve my problem; it's just not the ideal solution. Even though I only installed one topo map, to my device, it looks like 4 separate maps have been installed and I have to disable all four of them. (I don't know why the device treated the installed map as 4 separate maps, but that's what it did! Probably because of size). If there's a way for me to have finer control over the display of map data, I'd greatly appreciate an explanation on how to do that. I am aware that you can select the level of detaiI (most, more, normal, less, least) that a single map displays, but I'm talking about the interaction between maps. I'd rather the display of single map detail was based on map features rather than being based on level. I have to say, I'm not very impressed with Garmin's handheld device interfaces. So not intuitive!!! So not innovative!!!!