Lowrance electronic Lowrance GlobalMap 5500C - Manual (Page 11)

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to the WAAS satellites in orbit, but more about that in the upcoming
segment introducing you to GPS and WAAS.)
Your unit listens to signals from as many satellites as it can "see" above
the horizon, eliminates the weakest signals, then computes its location
in relation to those satellites. Once the GlobalMap figures its latitude
and longitude, it plots that position on the moving map shown on the
screen. The whole process takes place several times a second!
The performance doesn't stop there. Stored in the permanent memory
of each unit is a basic background map of the entire world. We lock it in
here at the factory — you can't change or erase this map.
The background map is suitable for many navigation chores, but for
maximum accuracy and much more detail, you need our optional map-
making software, MapCreate
 6. Some unit features — such as
searching for businesses and addresses — won't work without a custom
MapCreate map. There is so much detail in our background map (and
even more in MapCreate) that we'll describe their contents and differ-
ences in Section 3, Basic GPS Operations, on page 25.
Another portion of the GlobalMap's onboard memory is devoted to record-
ing GPS navigation information, which includes waypoints, event marker
icons, trails and routes. This lets you look back the way you came. Think
of this data storage like the hard drive memory in a computer or a tape in
a cassette tape recorder. You can save several different GPS data files,
erase 'em and record new ones, over and over again. Like any computer
file, these GPS Data Files (file format *.usr) can be shared between
Lowrance GPS or sonar/GPS units or even personal computers.
This GlobalMap has one more thing in common with a personal com-
puter. Just as computers have a floppy disk drive for storing and ex-
changing files, the unit has a slot for an MMC (MultiMedia Card) or SDC
(Secure Digital card) flash memory card. These solid-state memory de-
vices are about the size of a postage stamp, but can hold data ranging
from 8 MB to 1 GB in size. (Compare that to a floppy disk's 1.44 MB ca-
pacity!) This unit uses all that MMC space for two key GPS purposes.
First, you can backup your onboard GPS Data Files by copying them to
the MMC. Since the MMC is removable (like a floppy disk or a cassette
tape), you can store these GPS Data Files on a personal computer
equipped with an MMC card reader. (Or store them on a pocketful of
MMCs, if you don't have a computer.) Our MapCreate mapping software
can save, edit or create its own GPS Data Files, which can be copied to the
MMC and then loaded from the MMC into the unit's memory. (NOTE: No