HOW MUCH MAP MEMORY DO I NEED?
By Richard
Wilson
April 24, 2002
Only the user can determine the amount of memory required for the GPS receiver. It depends upon the area to be covered, the type of usage, the MapSource program, and a number of other things. Using Fishing Hot Spots to cover all the lakes in Kentucky requires only 1.7 Mb of memory. To cover just the city of Los Angeles in MetroGuide requires about 30 Mb. This article is intended to help make the decision as to the amount of memory needed for a particular application.
Most maps are in the shape of a rectangular block, and the dimensions of each block vary according to the amount of information and detail in that particular area. The maps can be previewed to see the area covered, and also the amount of detail in the map. To see this go to www.garmin.com/cartography/mapSource/ and follow the directions for Map Viewer found on that page. Unfortunately, this does not give the memory required for the individual maps.
Some of the Garmin GPS receivers have built-in map memory and the description of the unit on the Garmin site will give the amount of memory in the unit. Others have no internal map memory, but use a data card that is inserted into a slot. These cards are either pre-programmed, such as the BlueChart maps, or blank cards that are user programmed from MapSource on CD-ROM (BlueChart maps are available in both forms.). The blank cards are available in 8, 16, 32, 64, or 128 Mb.
It takes about 12 minutes to fully load an 8 Mb data card using the serial port from a PC. The process erases the card first, and the computer must build a map set and index files before it can load. The whole process takes about 15 minutes. The time increases proportionately with the amount of memory, so a 32 Mb card will take a little less than an hour, and a 128 Mb can take nearly 4 hours! This assumes selecting enough maps to fully load the card, but loading just 8 Mb into a 128 Mb card will take about the same time as loading them into an 8Mb card. The erasing takes a little longer in the larger card.
Data cards can also be programmed with a USB Data Programmer, available from Garmin or Garmin dealers. The loading time is cut drastically and a 32 Mb card is fully loaded in a few minutes instead of an hour. To load user defined waypoints and routes from MapSource to the GPS receiver requires the use of the PC serial port since the cards are only used to hold map data.
The chart below gives some map size information that should help in determining the map memory size required.
| MapSource Program | Map Area 1 | Largest Map | Typical Map |
| U S MetroGuide | Rectangular Block | 2.89 Mb | 0.50 Mb-2.00 Mb |
| U S Roads & Recreation | County | 0.522 Mb | 0.10 Mb-0.25 Mb |
| Fishing Hot Spots | Single Lake or Section of Great Lake | ||
| BlueChart | Rectangular Block | ||
| U S Topo Maps | Rectangular Block | ||
| Points of Interest | Rectangular Block | ||
| U S Waterways & Lights | Rectangular Block | ||
| City Navigator 2 | |||
| City Select 3 |
Notes:
1. The map area varies depending upon the number of
features and details in the
area. See the Map Viewer
on the Garmin web site for the particular
area of interest. www.garmin.com/cartography/mapSource/
2. City Navigator is not for sale individually. It is
included with Street Pilot III.
3. City Select is not for sale individually. It is
included with GPS V.
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