13. Routing Engine Performance

All the bells and whistles aside, what really matters on any GPS is the quality of the maps, and how well the GPS figures out how to get from point A to B..

The single most common complaint I hear is "the GPS took me on a crazy route that I would never have chosen", and "that definitely was not the best/shortest way."

Arguably the most critical components of any turn-by-turn GPS navigation system are the routing engine and map accuracy. The routing engine is the software on a GPS that decides which route the unit should choose to get from point A to point B. Many people falsely assume that simply having the same maps on two GPS devices will result in the same routing choices. Not so, as there is a great deal of math and decision-making involved when calculating the "best" route. Not all GPS devices are created equal, and side-by-side comparisons often show that two similarly priced devices with the same maps can produce very different routes.

Not surprisingly, this also one of the most difficult and complex aspects for GPS manufacturers to get right, and is the aspect of GPS navigation that is least well understood by consumers. Nevertheless, routing engine quality should be at the top of any GPS buyer's checklist.

There is a lot more to a routing engine than just the maps used. How a given GPS will determine the "best" route is the result of not only the mapping data, but also how many additional data points, or attributes, are factored into the equation. For example, are certain roads closed after hours or on the weekend? What is the average rate of speed for a given road? Statistically speaking, more accidents happen when making left turns as opposed to right turns -- is the GPS unit factoring that into the route? Each company takes all this data and compiles it in different ways, making unique decisions about what data is more important than others. The number of attributes used varies depending on how much money the manufacturer is willing to spend on their mapping data. For example, a full NAVTEQ map database that includes all available attributes can cost the manufacturer twice as much as a basic set of attributes.

All Magellan and Garmin GPS units use NAVTEQ mapping data, while TomTom uses Tele Atlas.

To test the Navigon 7100's routing engine, I entered three different trips of varying distance in three different regions of the United States and compared the Navigon's results to a Garmin nuvi 760 and a TomTom GO 720.

Our first test took us along the Northeast, starting in Southbury, CT and ending in New York City:

Navigon's 7100, Garmin's nuvi 760, and TomTom's GO 720 all get us successfully to our destination address in New York, but only the Garmin nuvi 760 has us arriving with the destination address on the right (correct) side of the street. The Garmin nuvi and Navigon both pick similar routes, but the Garmin provides more detailed navigation instructions, and is also the only GPS to announce what side of the street our destination address is on.

TomTom's GO 720 faired the worst in this test, giving less detailed instructions and putting the destination address on the opposite side of the street where we would have to make an illegal U-turn to arrive at the destination address. Also, TomTom uses yards instead of feet - a measurement less commonly used here in the Units States (probably makes good sense elsewhere, however).

Just for comparison, I plotted the same route on Yahoo and Google Maps: Yahoo! Maps (not shown in the table above) chooses a route identical to Garmin's route, but estimates the trip will take 3 minutes longer (1 hour 22 minutes) than Garmin estimates. Google Maps also chooses the same route as the Garmin nuvi.

So far Garmin's nuvi is in the lead. However, sometimes a GPS that routes perfectly well in one area can perform terribly in another region. Our first test used a trip that was approximately 80 miles in length and took us from Connecticut to New York City.

For our second test, I started out at Fry's Electronics in San Jose, California and entered a destination address at 300 Grove Street in San Francisco (about 46 miles in distance):

Again Navigon and Garmin choose almost identical routes, with TomTom choosing the worst route.

Garmin's instructions are more detailed, but the Navigon did produce a good route that's on par with Garmin's. The Garmin slightly edges out the Navigon in this test for arriving with the destination on the right side of the street, displaying what side of the street the destination address is on, and giving clearer, more detailed navigation instructions.

TomTom again has us arriving on the wrong side of the street, with our destination address on the left.

For the third test, I chose a short, 3-mile trip from Beacon Street in Boston to Cambridge, Massachusetts:

Garmin faired the best in this test, choosing a route that's slightly longer but shorter drive time, but all three GPS units placed us on the wrong side of the road at the destination address.

Navigon chose a better route than TomTom.

TomTom's GO 720 unit performed poorly in all three routing engine tests, producing the longer routes and putting us on the wrong side of the street in all three tests. Navigon faired well, choosing consistently solid routes. Only Garmin's GPS unit displayed what side of the street our destination address was on.