Don’t let your SatNav drive you up the garden path

Using a Satellite Navigator, commonly know as a GPS machine or Sat Nav, does not guarantee you will find your destination successfully or without incident.

There are two ways to program a satellite navigator to locate a specified place, either by typing in an address or a coordinate. Typing in postcodes works well in the UK where they are street specific, but French postcodes cover an entire town and its surroundings. If you need to use Postcodes in France, use the street and village name too.

Types of coordinate

When you want to pinpoint an exact location, you need a coordinate. To complicate this there are three commonly used coordinate types:

Degree Decimal Minutes, written as: N51º04.798’ E001º08.331’

Degrees, Minutes & Seconds, written as: N51º04’47.88” E001º08’19.86”

Decimal Degrees, written as: N51.079967º E001.13885º

Guidebooks may use any one of the above types of coordinates.

Vicarious Media uses the Degree Decimal Minutes format, also known as true GPS (N51°04.798’ E001°08.331’) in its All the Aires Guides. ACSI uses the GPS format Degrees, Minutes & Seconds (N51º04’47.88” E001º08’19.86”). Whilst Camperstop Europe uses Decimal Degrees (N51.079967º E001.13885º). Ensure your device accepts all three formats.

Degree Decimal Minutes, N51º04.798’ E001º08.331’ and Degrees, Minutes & Seconds N51º04’47.88” E001º08’19.86” look very similar. It is imperative to make sure you are using the correct format. We recommend that you test the three different types of coordinates to make sure the satellite navigator identifies the correct location, the following coordinates all locate Vicarious Media’s premises at Shorncliffe Industrial Estate in Folkestone:

N51º04.798’ E001º08.331’

N51.079967º E001.13885º

N51º04’47.88” E001º08’19.86”

By looking at the symbols indicted on your satnav you can identify the type of co-ordinate. If the symbols are not pre-filled, you must enter every symbol when you enter the coordinates.

Converting GPS Co-Ordinates

If your satellite navigator only accepts one type of GPS co-ordinate, it is possible to convert one type into another.This involves a little maths, so get a pen, paper and calculator. 

Changing Degree Decimal Minutes into Decimal Degrees. To convert N10º12.345’, ignore for now the degrees value and divide the minutes, everything after the degree symbol, by 60. In the example N10º12.345’, the minutes (12.345) are divided by 60 = 0.20575. Add the degrees value and directional letter (N10º) to the front of the new decimal (.20575) and the answer is N10.20575º.

Changing Decimal Degrees into Degree Decimal Minutes. To convert N10.12345º, ignore the degrees value (see above) and consider the decimal part of the degrees, everything past the full stop (.12345). Multiply 0.12345 by 60 = 7.407’. The number to the left of the decimal point (which may be one or two digits) represents the minutes, while the decimal number to the right of the decimal point shows the decimal minutes. Add the degrees value and directional letter and the conversion is N10°7.407’ minutes. To avoid possible confusion, minutes are always specified by two digits before the decimal point. This means that 7.407’ minutes is written (and entered into your satellite navigator) as 07.407’. So the answer above is correctly given in the form N10º07.407’.

Changing Degree Decimal Minutes into Degrees, Minutes and Seconds. To convert N10º12.345’, simply multiply the seconds, the very last part of the coordinate, by 60. Ignore the N10º12 and multiply .345 by 60 = 20.7. The 20.7 is added to the end of the N10º12’ to make N10º12’20.7”. To convert Degrees, Minutes and Seconds into Degree Decimal Minutes,simply divide the 20.7” by 60.

Both parts of the coordinate must be converted and it is imperative the correct letter is assigned to each part and the decimal point is put in the correct place. However, when choosing a satellite navigator I would strongly recommend that you buy one that takes all three coordinate types. It makes life much simpler!

When you buy your satellite navigator, ensure you find out where you input the GPS coordinates, usually in settings, and which types it can take. Do not take a sales representative’s word that the machine accepts coordinates.

Don’t let your Sat Nav lead you on a merry dance

The satellite navigator will be set to its default settings when you take it out of the box and you may wish to change some settings to suit your preferences. Often you can choose to avoid toll roads or choose the shortest route, the fastest route or main routes. It is important to realise that all options have their shortcomings. If you select ‘fastest route’ the satellite navigator will select country lanes with a national speed limit of 60mph over main routes restricted to 40mph. If you select ‘shortest route’ the routes are likely to include narrow country lanes up and over mountains; we have even been directed to drive off-road down green lanes. When you are underway and the satellite navigator directs you to turn off, always assess the road before turning into it and be prepared to turn around if necessary. Many towns now ban motorhomes from routes or roads, so check for these signs too. If you avoid Toll routes, then one-off toll bridges and tunnels will be avoided, which could be a very long way around.

Before you drive off blindly following your satellite navigator’s instructions, select your destination and preview the chosen route. This will allow you to asses, ideally against a map, that you are heading in the right direction. You may have to input some ‘via points’ at strategic junctions if you want to make the satellite navigator choose specific roads.

Finally, read the directions in All the Aires France. This will tell you if the GPS co-ordinate in directly on the site or slightly off. Exact co-ordinates are fabulous, but there is no point using a coordinate under a road bridge as the Sat Nav will often choose the road above. The directions will also warn you if it is best to follow the signs at the destination to avoid Sat Nav taking you though some difficult streets.

Further Infomation

This information is an abridged version of Chapter 4 from the essential Go Motorhoming and Campervanning.