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How to Evaluate GPS Solutions for Your PDA
 Posted August 2003 by Tong Zhang, Senior Editor

With more and more GPS packages coming out for the PDAs, PDA users can enjoy a selection of products from which they can pick the best to suite their needs. But what process does one go through, especially for a user who is new to the GPS solutions on PDA, to pick the best package? Here is a short guide to put you on the right track. To learn more about GPS, read our GPS FAQ.

There are generally three major components in a GPS solution that you should evaluate: the GPS receiver, navigation software and map data. We will go over each aspect and give you some advice on how to do the evaluation.

GPS Receivers

Often GPS solution vendors re-brand GPS receivers from OEMs (original equipment manufacturers). Almost all the current new GPS receivers are 12-channel parallel receivers. A12-channel parallel receiver can track up to 12 GPS satellites and it tracks them with dedicated hardware for each satellite, which leads to a faster fix. In theory, you only need 4 satellites to have a 3D fix. Currently there are no more than 11 GPS satellites (space vehicles) in our hemisphere, and it’s not unusual if you have only 5-6 satellites in view. So the 12 channel GPS has more than enough separate hardware to track each satellite in sight.

Having 12 channels in your GPS makes the calculation faster, but not necessarily more accurate. No GPS is 100% accurate. You can read our GPS FAQ to learn what affects GPS accuracy. Essentially you can get anywhere from 10 meter to hundreds of meters off the target. You can’t do anything about DoD jamming satellites, but you can make sure that your GPS receiver gets a very good access to the sky. Recently with the implementation of WAAS (Wide Area Augmentation System), a GPS receiver with WAAS enabled can get a very accurate location fix by correcting errors caused by Ionosphere, Ephemeris, Clock and more. (Again, read our GPS FAQ on WAAS). Some receivers claim that they can get within less than 3 meters of the actual location, which is very accurate for driving navigation purposes. Please note that WAAS currently only covers North America. The European and Asian systems will launch starting in 2004. I have not seen any DGPS (Differential GPS) bundled in PDA GPS packages, only in stand-alone GPS products from companies like Garmin.

So what should you do when you evaluate a GPS receiver? Since you can’t try the product before purchase, you can choose a WAAS enabled receiver if you need higher accuracy. You should also read multiple reviews on the receiver and see what the reviewer’s experience is like. One reviewer might experience different conditions than the others. If they all have good results, then you should be able to trust that receiver.

Navigation Software

Usually the navigation software is considered the crown jewels of the GPS package by your GPS vendors, because this part is developed in-house, as opposed to licensed from other vendors. Navigation software interfaces with your GPS receiver and hooks into your map data, providing users with a easy-to-use user interface that shows you the GPS status, allows you to plan your trips and provides you with driving guidance systems.

Each GPS solution looks a little different and has various bells and whistles that the others don’t have. You can often easily find demos of the navigation software on GPS vendors’ sites. I would suggest that you take a full advantage of these demos and evaluate all the important aspects of the navigation software, such as route planning, re-routing, guidance features, etc. For more GPS navigation software info and screen shots of the user interface, read our GPS product reviews.


Many PDA GPS vendors license map data and POI (points of interest) databases from one of the big map makers. Most of the maps are made in a similar way: get the basic info from the government, like the county planning agencies, then incorporate that data with aerial photos, satellite images, and get road updates from professionals and consumers. Each map maker does something a little different during this similar process and tries to get as accurate map data as possible. For example, the data from the planning agency is good, but not accurate because some buildings or roads may never get developed and the ones, which have been built, take some time to make it into the report. So some map makers will use USGS data, Census Bureau data, even police and fire department to crosscheck the map data. Other map makers develop better ways to incorporate photos data into their vector maps.

You should know that there isn’t a single digital map that is 100% updated. What can you do when you evaluate a GPS solution that is bundled with certain map maker’s data? You can often sample the maps of an area you are very familiar with. This isn’t a fool proof as map coverage varies in different areas. But it could be a good indicator of how detailed and extensive the map data is. Here is a list of some major map makers and where you can sample their data.

NavTech is one of the biggest map makers. They supply most of the maps used by all major automobile GPS systems in the US, and provide data to The way they update their map is by using their field forces. They have over 100 field offices staffed with analysts and engineers who drive miles and miles to record fresh road info and POIs. Their map database is updated quarterly. NavTech started out with only major city street-level maps and later added maps to cover the whole country. Their street-level info includes many road segments such as one-way street, turn restrictions and more. You can use to sample NavTech’s map data.

Tele Atlas is another big map maker who offers both US and international map data. They supply their data to many transportation companies. They also have a large field force that updates the map data and POI database. Their new map database has a pre-eminent traffic feed with over 350,000 traffic reporting locations embedded into the maps. You can sample their maps on this site:

Rand McNally has been providing print maps Road Atlas for a long time. StreetFinder, their digital map package, is very popular, but they are mostly purchased from Tele Atlas and NavTech. They also bought Thomas Bros. who makes very detailed street-level maps for some parts of the US. Their city guides have a very extensive POI database including many categories that other POI databases just simply don’t have. You can sample their maps right on Rand McNally’s web site.

Tiger, (Topologically Integrated Geographic Encoding and Referencing system), isn’t a name you see often in map bundles, but it contributes to many map-making processes. Tiger maps are the product of the Census Bureau and are the source of the US government’s map data. The maps are based on USGS data and are not updated often. But their data does get incorporated into other map packages. Here is a map view where you can check out the map samples.







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