My wife and I have been using a Garmin GPS device in our vehicles for over several years. Of course we would suggest anyone using these devices become as familiar as possible with them near home before using them in an unfamiliar setting. Asking for directions to places with which you are quite familiar is an excellent way to find out what they can and can't do. The device's default settings are there for a reason--don't change it or forget to reset it without justification.
These devices are not perfect by any means. New roads or points of interest may not be on your device's internal map (or they are but have gone out of business); addresses may only be approximate; the satellites the device depends on may be hidden by tunnels, walls, or buildings (forget about using it in downtown Dallas for example); or your location may be off by 50 to 75 feet or up to 0.25 miles (personal longest). Software in the GPS assumes you are on a road if you are near one. Parking lots are usually missing as are ways to get in and out of many shops or businesses. Use your own judgement before following its first two commands.
The picture shows a cartography error in that Germantown Road doesn't line up going from Mississippi to Tennessee. We were directed to make a sharp N (or reverse N) turn when none was there (hard left turn in upper left of screen). This was corrected in May, 2011.
Navteq maintains the maps Garmin and several other makers of GPS devices use. If you find something that doesn't agree with what your GPS says, take a digital picture of it (if appropriate) and let Navteq know about it.
Accuracy as to the exact place of a street address varies. If street numbers are assigned according to the number of yards (3 ft) from a section line or all lots on a block are the same size, the given location should be quite accurate. Perhaps everything was renumbered but the house you are looking for kept its old number. If the size of the lots varies or the address is not on a block, what your GPS gives you may only be in a large ballpark. If you are looking for an address on a highway which passes through town, research it before your trip as the address could be off by several miles.
Your GPS and your PC
I did not know about this feature before choosing Garmin, but I wouldn't take anything for it now. As you build your list of favorite places, they are stored on the file E:/Garmin/GPX/Current.GPX (your drive letter may be different) as well as tracks of where you have been recently. Of course, a USB cable to connect your GPS to your computer is essential. You can copy this file to your PC (mine is in the "Garmin" folder under "My Documents") as backup or as a way to move everything to a newer unit.
Before mentioning the programs which can work the Global Positioning eXchange file, you might want to request all latitude and longitude to be in degrees to four or more decimal places--forget minutes and seconds. Your GPS as well as Google Earth and MapSource all allow you to do this. If you have to convert something with minutes and seconds, divide the seconds by 60 and add to minutes, then divide minutes by 60 and add to degrees. See the conversion at the bottom. One hundred-thousandth of a degree (0.000010) is less than 44 inches latitude and even less for longitude, so you can round off the 6th digit Google Earth gives you when plugging coordinates into the GPS.
The program Google Earth can read your file from your device or maybe from your PC (note on this later). Garmin MapSource (installed on your system when you update your maps) can read the file from the device or PC and can write it to either location. When on the device all carriage returns and line feeds are stripped away (a file in this format is very difficult to modify), but these are restored when writing this file to the PC. I have found Google Earth sometimes can't read this formatted file, but it doesn't need to. Once read, your favorite places will all appear to have a flag and label when you bring them up on the same maps that are on your GPS. If a favorite place needs to have its position changed, note the coordinates of your cursor when you have moved it to the driveway of the place, just off the road. When you bring up MapSource and select that favorite place (waypoints here) by double clicking, you can change the coordinates and click on OK. Write the file back to the GPS and your hard drive and you're done. Both programs can show your tracks. MapSource defaults to Garmin DataBase format, but its Save As selection has many options.
If you plan to visit various specific places on a long trip, first clear your list of "Recent Favorites" from your GPS. Select those places and GO, but back out to enter a new destination. Once a destination and route has been calculated, that destination is added to "Recent Favorites"--since you cleared it out before starting all destinations will be in that small list.
A while back my wife visited a high school classmate at a bed and breakfast near her friend's home in Texas. The owner only provided turn-by-turn instructions from Dallas and, when we found the exact location with Google Earth and entered it into her GPS, it wanted her to leave the Interstate while still in Louisiana! To get around that we found a via point close to the Interstate just east of the turn-by-turn route. When forced to use that via point, the route stayed on the Interstate until it got close to that point and shortly joined the given route.
GPS and Time
Your GPS is probably the most accurate timepiece you own. When it is necessary to set or reset any clocks or watches or date/time on your PC, select Tools and World Clock. Many digital clocks will set the seconds to zero whenever the minutes are changed so you can be ready to make the last change to the minutes when the instant it changes on your GPS (and, of course, when the seconds are zeroed).
Even when you are driving on a quite familiar route, the Estimated Time of Arrival could be helpful to anyone waiting for you. On routine (I've driven this a million times) trips, it won't be worth much but may sometimes be helpful when going to familiar destinations starting at a different location than home.
This program should be the one with which you start. This can update itself as well as the software on your Garmin GPS. It warns about updating the software on a GPS if it doesn't have a full charge in its batteries, but with rechargeable batteries (the norm in automotive devices) the power from the USB cable will keep them charged up. The program can be used with many Garmin GPS devices (I've used the same program on four of them) and will update the software as needed.
Ever have trouble finding your car after leaving it in a
really big and unfamiliar parking lot or on the side of the street in the French Quarter of New Orleans?
Before leaving your car, save your position and take your GPS with you. Set your GPS to pedestrian
mode to walk back (and set it back when you drive off). Settled in to your room while on vacation or
business trip? Get in (or at least in front of) the best parking place for your room and save the
position. It will make getting back much easier. Many more helpful tips can be found on
Gary Hayman's site.
A new webpage will show you the fifteen trackpoints closest to the coordinates you specify. If you specify the correct hemispheres, it will not be necessary to enter negative degrees. Use degrees with decimal points only and only formatted .gpx files like those created by MapSource. Click here.