Lowrance electronic Lowrance GlobalMap 5500C - Manual (Page 12)

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matter where they come from, GPS Data Files must be loaded from the
MMC into memory before the GlobalMap can use them.)
The other key GPS use for MMCs is storage of special high-detail, cus-
tom maps, which you can produce on your computer with our MapCre-
ate software. These MapCreate custom maps contain much greater de-
tail than the basic background map. These Custom Map Files (file
format *.lcm) can also be shared between Lowrance GPS or sonar/GPS
units and personal computers.
This unit automatically reads Custom Map Files directly from the
MMC or SDC. To use a custom map, all you need to do is slide an MMC
containing a map into the GlobalMap.
Introduction to GPS and WAAS
Well, now you know the basics of how the unit does its work. You might
be ready to jump ahead to Section 2, Installation & Accessories, on page
11, so you can mount your GlobalMap and plug in the power. Or you
might want to see how our text formatting makes the manual tutorials
easy to skim. If that's the case, move on to "How to Use This Manual"
on page 8. But, if you want to understand the current state of satellite
navigation, look over this segment describing how GPS and its new
companion WAAS work together to get you where you're going.
The Global Positioning System (GPS) was launched July 17, 1995 by
the United States Department of Defense. It was designed as a 24-
hour-a-day, 365-days-a-year, all weather global navigation system for
the armed forces of the U.S. and its allies. Civilian use was also avail-
able at first, but it was less accurate because the military scrambled
the signal somewhat, using a process called Selective Availability (SA).
GPS proved so useful for civilian navigation the federal government
discontinued SA on May 2, 2000, after the military developed other
methods to deny GPS service to enemy forces. Reliable accuracy for ci-
vilian users jumped from 100 meters (330 feet) under SA to the present
level of 10 to 20 meters (about 30 to 60 feet.)