The following information my be helpful.
My Garmin GPSMap 76Cx has a page, which will provide me with the information. This should also work for the 60Cx, 60CSx, and the 76CSx. If you have a (x) model other then listed please check and let us know if this process works with your unit.
My 76Cx has an after market 2 GB micro SD card installed. The Base Map is factory installed and does not affect the capacity of the micro card. Based on my experience you cannot fill the card to capacity because the unit needs operating room.
Select the Main Menu Page>Setup Icon>Enter>System>Enter>Menu Button>Card Info>and you get the Card Information Page.
The first line tells me that my card is 96% full. If you push it much beyond this point the system may not work and you will have to create a smaller Map Set.
It shows that I have 1843.9 maps installed.
Saved Tracks are using 2.04 MB of memory.
Miscellaneous Space 2.04 MB.
There is 65.97 MB of Free Space.
Total Space use 1848.2 MB
The map count is in conflict with what Map Source on my computer is telling me. Map Source says that I have 1997 maps installed. I do not have an explanation for the difference.
I have loaded maps from Map Source US Topo, and Map Source City Navigator v8 on the Micro SD card. In this case I have inserted the micro SD card in the adapter that came with it. I then inserted it into the SD card reader slot in my computer. The computer tells me that a new device has been added and I have the computer find the software to install the card.
US Topo maps cover approximately 1/3 of Alaska, the Western United States from Canada to Mexico, to the Eastern boundaries of Montana, Wyoming, down the East side on New Mexico just below I-40, and then Eastward to the Arizona Stateline and then down to the Mexican border.
It is easier to identify what I have not installed from City Navigator v8, Alaska, N. Dakota, Missouri, Minnesota, and parts of Iowa, Oklahoma, and Wisconsin.
City Navigator is higher hierarchy software the US Topo. If the unit is showing City Navigator the US Topo maps for the same ground will not be shown. If I want to view US Topo I need to go to the menu on the Map Page and hide City Navigator. In turn City Navigator and US Topo are higher in the pecking order then the basemap.
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Some answers from Garmin:
Question: Is there a limitation as to how many maps can be loaded to the micro SD card for my "x" model gps?
Answer:
Currently the expandable memory devices are limited by the size of the data card being used in the device or up to 2025 map sets.
Last modified on: 06/27/2007
Question: What is the largest size microSD card that I can use in my X-series GPS unit?
Answer:
At this time, the 2 GB cards are the largest microSD cards that can be used for the X-series GPS units. However, the X-series GPS units are not compatible with the San Disk Ultra II cards and therefore we do not recommend using the Ultra II micro SD cards with any of the X units.
Last modified on: 06/01/2007
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Is the 2 GB a moving target? It was not long ago the largest card the unit software would recognize only 1 GB and then Garmin updated the software to recognize the 2 GB card. Recently I have been seeing 4 GB micro SD cards at sale prices. Will Garmin again upgrade the software for the (x) units to recognize 4 GB of memory?