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Who to Blame for Bad GPS Routes?


Quite a few people have been asking us questions or making statements that leads us to believe there are some misconceptions out there about how GPS devices calculate routes, and what part of the process is responsible when an obviously bad route is being suggested by your GPS. Perhaps this should be appended to our 10 GPS Myths post. Let’s dig into this a little bit and figure out where the map data provider, the GPS device, and the GPS software play a role in calculating routes.

Let’s start at the beginning of the process, and I’ll use the analogy of traditional “paper” mapping and how a human might figure out the best route with a paper map.

Mapping companies are constantly out on the roads creating the underlying data that is used in GPS devices. They drive the roads, classify the roads, mark where certain turns are allowed, identify one-way roads, etc. All of this data is aggregated and delivered to the GPS device manufacturer as raw data.

Each GPS manufacturer then takes that raw data and converts it into a format that their GPS devices can work with. This is one of the reasons why maps from one company normally don’t work on the GPS device from another company. So the GPS manufacturer puts the data into a format that works for them, and loads the mapping data on the device. So the paper equivalent is someone handing you the paper map.

Now comes the software on the GPS device. This is where routes are calculated. Each GPS device has software onboard written by the GPS manufacturer which looks at the data to determine the best route.

If this was a paper map, here is where each person reading the map would look at the roads and try to figure out which is the best way to reach their destination. They might say to themselves, “the shortest way is via these two streets, but if I travel a little further I can take this highway where the speeds might be faster and thus make up for the slightly longer distance.”

There are certain things we, as people, have learned about picking routes. As in the example above, the fastest route might not always be the same as the shortest route. Other factors can also impact the “fastest” route such as turns…. the more turns you need to make the more likely the route will be slower waiting for traffic at intersections and traffic lights. If you do need to make a turn it is often easier (faster) to make a right turn than it is to make a left turn in countries where you drive on the right side of the road.

Each GPS manufacturer writes the code which tries to figure those things out. So what can we conclude from this? Even if two GPS manufacturers are presented with the exact same set of data from the same map vendor each GPS device could calculate a different “fastest” set of directions for the same route.

People often see with GPS devices and online maps that different programs make the same “mistake”. Also, some might assume that if one GPS device that uses NAVTEQ maps and makes a “mistake” in the best routing that another GPS device also using NAVTEQ maps would make the same mistake. This isn’t necessarily correct.

It could be that the mistake was due to an improper calculation of estimated road speeds that came from the map provider in which case most GPS devices would make the same mistake. However it could also be that the GPS device didn’t see the same problem with the route that you did, or that it is accounting for road characteristics that you didn’t account for.

To summarize…. just because one GPS device gives you a bad route doesn’t mean that all GPS devices which use the same mapping provider will calculate the same route.

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