Garmin GPS and the Swedish 1:100 000 Fjällkartan
Settings at the GPS
In order to use the Garmin GPS together with the Fjällkartan, you should check two settings in the Menu:
In Menu > Navigation set :
Position Format to : Swedish Grid and
Map Datum to : RT90
Now the settings correspond to grid and map datum of the Fjällkartan. The GPS Handbook explains what these settings mean.
In the picture below, which shows a small part of a Swedish "Fjällkartan", thin black lines can be seen, and they represent the "Swedish Grid". They enable us to transfer coordinates from the GPS to the map, respectively to read coordinates in the map for an upload to the GPS
Looking up a Position in the Fjällkartan for an Upload to the GPS
The following examples are valid for a 1:100 000 map. At the margins of the Swedish Fjällkartan one finds several sets of numbers:
At first, a look at the numbers that we do not need: the brown digits at the upper margin (19 degrees 20 min) und the corresponding brown vertical line indicate the regular longitude. We ignore them, because we want to work with the Swedish grid. The Swedish grid is indicated by the thin black lines, which stretch across the map in distances of 2 cm, and they are well appropriate for practical work. Now, a closer look at these numbers.
The upper right corner is marked with 1650 and 7548. These numbers also give the eastern longitude and northern latitude, but in the Swedish grid with map datum RT90, which we have set in the Garmin GPS.
The distance between two of these black lines is 2 centimetres in the map, respectively 2 kilometres or 2000 metres in nature. The Garmin GPS shows these coordinate values in the display (compared to the inscription on the map) with three added digits, so it would show at this place:
East 1650000 North 7548000
We need to keep in mind that one unit in this display mode corresponds to one metre in nature. In the map, one unit shown on the display corresponds to one hundreth of a millimeter, or 1/1000 of a centimetre. That is a very important statement, you should better read it twice.
Now we try to read the coordinates of the Tarfala cabin from the map section below. At first, we look up the coordinates of the grid square. Luckily, two coordinates have been marked in this part of the map, otherwise we would have to follow the lines from the margin. So it is easy to find the grid lines 7540000 and 1620000.
What we need are the coordinates the lower left corner of the square containing Tarfalastugan, which then are
E 1616000 N 7538000.
From the left respectively the lower grid line of the square one can measure 1.35 cm in horizontal and 0.8 cm in vertical direction. One centimetre, as mentioned above, corresponds to 1 kilometre or 1000 metres or 1000 Units in des GPS display. So multiply the distances with 1000 (yielding 1350, 800 ) and add these numbers to the lower left corner to get the coordinates of the cabin, which are E 16173500 N 7538800.
It is more elegant and comfortable to use an appropriate software, scan the map, calibrate it by marking three positions, and then you are able to look up positions with the mouse. I bought the Fugawi program, which is not quite cheap. The computer procedure is not more accurate. The red square of the Tarfala cabin has a size of about 1 millimetre in the map, and this means 100 metres in nature. Even if you scan the map and click the positions with the mouse, you cannot measure more accurate. However, you have a better optical control and you avoid making mistakes that can occur when you type in the numbers you have measured with a ruler.
One of the most important questions in life is "where am I". If you are in Sweden, have a GPS and a Fjällkartan, the answer is easy.
Looking up a Position Shown by the GPS in the Swedish Fjällkartan
On the GPS, which has been set to "Swedish Grid/RT90" as mentioned above, you read the following coordinate numbers:
E 1616100 N 7538750.
At first you look up the 1616000 - 7538000 coordinate in the map above. The remaining rest of 100 units in eastern direction and 750 units in northern direction corresponds to 0.1 cm to the east and 0.75 cm to the north in the map, and thus we find that we are on the summit west of Tarfalastugan, which has an elevation of 1711 m.
Since the grid has a size of 2 kilometres, the position on the map is exact to roughly 500 metres, if you just divide one square visually into four parts. For some purposes this will be exact enough on a tour. For a more exact determination you need a ruler - in most cases, there will be one on your compass.:-)