I have a Triton and have played around very briefly making raster maps for it using TritonRMP. Each image is only viewable through a range of about 3 zoom levels though, and you need to add lower resolution images to the same file if you want a full range of zoom capability, which is sort of a pain. That type of map won't work on the Meridian Gold however, which is an old model (my first handheld unit in fact, that I purchased in 2002 and sold long ago.

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There are also ways to make vector-based Magellan maps but I never took the time to dig into these. Some discussion here:
http://www.tritonforum.com/forum/viewforum.php?f=32