I believe that the prior version or some version of the Garmin software did use maps contained in a sd card. I am not quite sure how it worked but their current version appears to use the live-data concept. Maybe attempting to keep maps current on SD cards was a pain or maybe people found using the cards inconvenient.
It may also be that the "convergence" of phone and active gps is not quite there yet. I find the recalc on my 8830 to be quite slow compared with my standalone Tomtom gps. Now part of that is probably the fact that the 8830 has to tell someone (the gps map purveyor) where it is when the route is "broken" and then get new maps via more data. I don't know if the route is even computed on the 8830 or back on some "mainframe" and then sent to the 8830. - just speculation on my part.
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