Our Sat Navs are great for stopping us getting lost. Whether it’s a TomTom, a Garmin or any other brand, being able to tap in an address and have the little device do all the planning gives us confidence and saves time working out routes.

The problem comes when we put in a postcode and the Sat Nav draws a blank. Luckily, it’s not too common an occurence, but setting off on a journey can be a little daunting when our navigator seems to think the destination doesn’t exist. There are a number of reasons why this can happen, so we’ve created a guide to why your Sat Nav is sometimes on the road to nowhere.

The Knowhow

Where does the map data come from?

The maps on Sat Nav systems are created from at least two types of source:

  • Licenced map data from cartographers such as Ordanance Survey or Navteq
  • Original data researched by the Sat Nav company; for example, TomTom own a mapping company called Tele Atlas that provides data for them

How is the map data updated?

Companies that make maps, and those that make Sat Navs, constantly perform their own research into new roads, town layouts and changes to existing routes. However, resources can mean that they can only focus on certain key towns and cities on a regular basis, or that less populated areas are visited on an infrequent rotational basis.

Taking into account the size of the country, the number of man-hours required to physically survey every road makes it impractical to ensure all data is constantly up-to-the-minute. To provide this level of service, the companies would need so many cartographers and surveyors that the price of their maps would become astronomical.

Instead, companies have to rely, in part, on information given by other sources; for example, satellite images, town planners, councils and even users. This helps them correct omissions, errors and focus on areas that need special attention during the next run of surveys.

Why aren’t all new streets included in the updates?

Town plans can change on a regular basis, and new roads are added as houses get built. As the data in your Sat Nav is based on an existing map and updated as the company receives new information, sometimes it can take a while for areas to be updated.

For example, a large housing estate may not be fully surveyed until it’s totally completed, even though parts of it are already populated. At other times, tracks that are unsuitable for vehicles may be listed as routes because they were originally classed as minor roads when the initial surveys were conducted many years ago.

In very rare instances, a location may be part of a "trap street". These are features included in maps to detect if someone is copying the data without paying for it. Often these are hidden in minor details that shouldn’t affect users, but occasionally a street may be deliberately renamed, or a route that doesn’t exist added, to protect the makers’ copyright.

What else can affect my Sat Nav?

  • System bugs can make your device produce the wrong information; keeping it up to date with the latest firmware from the manufacturer will help prevent this
  • Errors in the mapping data used can direct you to the wrong place; Sat Nav companies will often have areas on their websites where you can report these issues for correction
  • Postcodes can cover several addresses, sometimes on more than one street. Depending on your model, using a postcode may guide you to a street near your destination rather than the one you actually wanted
  • Your Sat Nav works by receiving GPS data. These signals can become weak or confused in some areas, leading your device to act erratically or think it is somewhere else. If this happens regularly, fitting a Sat Nav antenna can help boost the signal
  • A Sat Nav combines your GPS position with the available map data to provide your route. If roads have been mislabelled, closed or rerouted and the data hasn’t been included in an update, it will still try to use these roads

If you know a location near your destination, you can use that postcode to navigate to. Alternatively, you may be able to make use of the map functions of a computer or smartphone, before the journey or while parked, to locate a nearby area your device can find. Log any problems or errors you find, and it’s just possible the next update will help you hit the road again.

Updated On:

Nov 21, 2011

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