The Global Positioning System (GPS) allows positioning anywhere on the earth with an accuracy of less than 3 meters.
The receivers use signals from navigation satellites and do not transmit any data to the satellites.
The system is free, so the only cost is the purchase of the receiver and associated accessories.
With the development of sophisticated mapping units there's little point to getting a GPS receiver that does not support map
download capability.
Equally as important, is sufficient memory to hold a significant amount of map detail so you don't
have to be reloading the maps every time you go somewhere different.
I am particular to Garmin receivers.
They tend to pay a lot more attention to detail.
As an example, besides the obvious differences, all waypoints are stored internally under a single map datum.
What this means is that map datums are used for display purposes only.
You can store your location under one datum, and then return to the same exact location with any map datum selected.
I have not observed any other manufacturers that do this.
For those that are not familiar with map datums, they are used to describe the irregular shape of the earth.
Coordinate systems assume the earth is a perfect sphere and map datums make up the difference.
When locating yourself on a map, look at the map legend to see which map datum was used when creating the map and select this
datum on your GPS receiver.
This will ensure maximum map accuracy.
Garmin sells an extensive line of downloadable maps.
I own a topographic CD ROM set and a set of street maps.
While the topographic maps could hardly replace the utility of USGS 7.5 minute paper maps, they provide a level of detail
that I can't imagine doing without.
The street maps are incredibly useful.
Besides navigating to street addresses, intersections, highway exits, and cities, you can find points of interest anywhere you go.
For example, while sitting in your hotel room, you can find all of the restaurant nearby, including information about the type of
food they serve and their telephone number.
Of course, finding the restaurant is a breeze with the GPS.
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