So you've finally decided you're going to purchase a GPS unit. Now the only question is what to get.

In an ideal world, the GPS unit you purchased would be portable, have great battery life, be able to hold all maps in memory, give perfect driving directions, have a bright color screen, plan an alternate route in heavy traffic, be rugged and waterproof, and be able to communicate easily with other electronic devices. And, you would get all of this at an affordable price.

I have good news and bad news. The good newsall of those features are available on GPS systems. The bad newsno GPS system offers all of them on one unit.

When you're out shopping for a new GPS unit, there are four main types of GPS devices you'll encounter: the car navigation system, the handheld GPS, the boat GPS, and the PDA/GPS hybrid.

The Car Navigation System
Most luxury models now offer built in navigation systems - it's even standard on some. It's also becoming common to find a navigation system as an option for mainstream vehicles. However, if a built in system isn't an option for your new car, or if you plan on putting GPS in your current vehicle, there's always the dash mountable option. Companies such as TomTom, Garmin, and Magellan offer some of the more popular dash mountable GPS devices.

Features you're likely to get with an in car system include: a color screen; voice guided directions; information about gas stations, hotels, and other points of interest along your route; the ability to calculate a new route should you get off course; and the ability to get traffic information so you can avoid heavy congestion (frequently offered as a per month subscription service). Car navigation GPS tend to be the most expensive with built in systems costing upwards of $2000 in many vehicles. Good dash mountable devices typically cost around $1000 although less expensive options are available.

The Handheld GPS Device
The GPS devices designed for outdoor enthusiasts are the most affordable type of GPS unit. Low end models cost as little as $100. High-end models cost about $500. These units are great to have if you spend a lot of time hiking or camping. They are also the type of GPS units anyone who wants to start geocaching (http://www.gpsmaestro.com/geocaching) will want to use. Some of the features you'll find on a these units: base maps of parks, lakes and mountains where you plan on hiking; a built in compass, the ability to input coordinates; chart plotting so you can tell where you've been and can retrace your path if necessary; color or monochrome displays depending on the model; an altimeter; a rugged durable housing; and water resistance or full waterproofing.

One high end outdoor unit, the Rino series by Garmin, even offers a built in two- way radio, an NOAA weather receiver, and position reporting capability which allows you to see the position of all the people in your group that have one of the devices. You're even able to poll this GPS unit for its position if a member of your party should become incapacitated. If you want the capability to still have in-car navigation once in a while, these units can be attached to a laptop running navigation software to help guide you to your destination.

The Marine GPS
If you'll be spending most of your time on the water with your GPS, then a marine GPS unit is your best choice. Some of the features you'll frequently find on marine GPS devices are: color chart plotters; screens that are easily visible - even in bright sunlight; sonar capability; and onshore/offshore maps. Some new units even offer weather service integration with specific information for boaters, and automobile navigation so you don't need to purchase two separate units. Marine GPS units fall in between the portable outdoor units and the car navigation systems in price, with many good marine GPS unit costing around $1000.

The PDA/GPS Hybrid
If you're looking for a jack of all trades GPS device, then you may want to consider the PDA/GPS hybrid units. Many of these systems are full featured PDAs with built in GPS capabilities. You can also purchase a separate unit if you already have a PDA and just want to add on GPS. These separate units will connect to your PDA via Bluetooth, serial cables, or USB cables depending on the capabilities of your PDA.

The PDA/GPS units are great combinations for a person who is always on the move. They allow you to stay organized and will also guide you to wherever it is you want to go. The one drawback to this combination is that there always seems to be something that is sacrificed.

By purchasing an all-in-one unit, many times you get a pretty good GPS but only an okay PDA. If you purchase a top of the line PDA and then add a GPS receiver to it, you have the inconvenience of carrying along extra devices, along with needing more plugs to keep things charged. These setups tend to be more economical than in-car navigation devices though, running around $500 for all-in-one units to $900 if you decide to purchase a high end PDA and a high end Bluetooth device to synch with it.

Although there is currently not an ideal GPS unit that does everything perfectly, there are still many excellent options available. The trick to finding the right GPS for you is to decide how the GPS is likely to be used most often. If you spend most of your time on the road, then the in-car system is most likely your best bet. If you spend most of your time hiking or geocaching, then a portable unit will likely serve you better. If you plan on doing a little of everything, you may want to consider a PDA/GPS hybrid model.