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Can somebody explain to me how map projections work in GPS units?  It seems to me you need to do something, like set the GPS unit to the correct map projection before you load the map?  If you do, how do you know the projection of the map you loaded, such as the Ibycus data on this web site.  Or does Mapsource magically handle everything so you do not need to worry about that? 

One more question.  I just got my GPS and tried it yesterday, recorded a route, and changed the projection to the two most common I see (NAD27 and 83).  The position of the route relative to the map seemed to stay the same.  Are GPS units so smart they adjust everything realted to the map projection on the fly or was this a coincidence?

Thanks for the answer.

Basically I would like to get as complete possible logging/fire/dirt road information, without spending more money then needed.  I see three options, Garmin's 1:24,000 maps, Garmin's 1:100,000 scale maps, and the maps here.  Can anybody tell me how complete these maps are without extensive field testing?  Again the only data I care about is road data. 

Also, long shot. but I have to ask.  Can anybody tell me if City Navigator has good wildland road data?

My only experience is with a friend's GPS while in the coast range of Oregon, where Gramin's 1:100,000 maps have very complete road data. If the road data is that good everywhere, I would prefer to purchase the larger scale and get more states. Obviously though I would prefer giving a small donation over the cost of Garmin's maps.

Background. I have a Vista HCx that should be arriving in the mail tomorrow. I am asking for use on wildland fire.  Also since I plan on using the GPS with my motorcycle and bicycle, I may also order City Navigator, pending testing of the city road data from this site.

Thank you for your answer.