Primary Factor 101

The unofficial version

OK, what is it ?

"Primary factor" is a well known term among mountain enthusiasts. In short, it represents the vertical drop between one mountain and a higher mountain. You will have to follow the highest possible route between the two mountains, and the lowest point on this route is often refered to as "the saddle". Thus, mountain height - saddle height = primary factor.

Primary factor is also refered to as "prominence". David Metzler's definition is "Prominence is defined as the elevation difference between a peak and the lowest contour that encircles it and no higher summit". Metzler has posted a list of the World's top 50 peaks by prominence. Also make sure you check out, which contains everything you need to know about the subject.

Come again ?

Let's take the below picture as example:

We want to find Geitadalstind's primary factor towards the higher Ulvanosa. The saddle height is approx. 1090m (interpolated from the oppsite 1100m 20m contours in the saddle). The primary factor in this case is 1210m - 1090m = 120m. Imagine if the sea level rose to 1089m. Then you would see the only dry route you could walk between the two mountains. Ulvanosa's primary factor is determined by a higher mountain, and not Geitadalstind. 

In some cases, the "saddle" can be far away. For Sandfloegga, the highest point on Hardangervidda, you will find the "saddle" near highway 7 almost 60Km further northeast. This is the highest route to a higher mountain, in this case Hardangerjøkulen. It is not always trivial to determine saddles that are far away. To find the high route, in general, follow the high terrain, and never cross rivers (a river implies that there is a higher point somewhere). 

Interpolation, you said?

The M711 map series from Statens Kartverk operate with 20m contours. When a saddle is found, one look at the last contour on each side of the saddle. Let us assume they are the 1100m contours (as in the example above). The saddle height could be anywhere from 1081m to 1099m. We don't know (unless saddle height is known), and in general it is fair to assume a 10m interpolation. As such, the above saddle is defined to be 1090m. This is not exact science, but gives a fair impression of the prominence. When available, I have used the maps that operate with 5m contours. In some cases, there is a noticeable deviation between the two maps, but I have put more faith in the 5m maps with a greater level of information. 

OK, I follow, but what's the big deal?

There are some interesting aspects to it. Mountains with a large primary factor in most cases have a superb view. And we like superb views. So if you want to know where to get views in Hordaland, then take a look at my list of mountains, sorted by primary factor.

Many go after mountains based on their height. In the case of Hordaland, the majority of high mountains are found on Hardangervidda or around Finse. And honestly, only a few are truly great to look at. When primary factor is taken into consideration, one gets an alternative list of mountains, spread across Hordaland. If someone asked me to name the 50 most spectacular mountains in Hordaland, then most of those mountains would be among the top 50 on the primary factor list, above. With only a few exceptions.

When I wanted to identify all mountains in Hordaland, I had to use some criterion to distinguish the obvious mountains from the lower hills. I settled for  300 feet as the primary factor (close enough to 100m), a height frequently used around the world (In places like the Andes and Himalayas, this number is higher). 100m agreed with my personal view on the definition of a Norwegian peak. On my web pages, I have not unfortunately not distinguished between the words "mountain" and "peak". You could find several peaks on one mountain, and these peaks may have a primary factor of 100m or more. The Geitadalstind/Ulvanosa picture above is a good example of this.

Typical for Hordaland, and probably also for other Norwegian regions, is that people have put names on the mountains they see from down below. Once on top, you may find that the mountain continues rising towards a higher point, further away. The Folgefonna glacier massive is a good example. 

You will find named points around the entire massive, but most of these points are just rock that marks the end of the mountain massive. By applying the 100m primary factor, these named points exclude themselves from my list of Hordaland mountains. 

In the process, I have significantly improved my map reading skills, and my knowledge and understanding about the Hordaland terrain. Of the approx. 670 mountains above 300m (which was my height criterion), I found that more than 400 mountains had a primary factor of 200m or less. This indicates large massives, with little drop inbetween the tops. It would also suggest that few mountains are truly characteristic (viewed from all angles) and unique. The Hardangervidda and Stølsheimen mountain ranges are good examples of this. As such, there is all the more reason to find the characteristic mountains, and this is what I believe I have done through sorting my primary factor list.

Only two mountains have a primary factor of more than 1000m (Folgefonna and Hjortahorgi), while 29 mountains have a primary factor of more than 500m. All these mountains are well worth a visit.

There are mountains with a primary factor less than 100m, that should not be excluded based on this technical angle. A very good example is Laurdalstind near Rosendal:

Laurdalstind, to the right of the river, is a spectacular view from below, and one of the most challenging mountains in Hordaland, on the easiest route. It has a primary factor of only 57m, but gave me a memory for life. 

So, you care. Does anyone else?

Apparently. My good friend Petter Bjørstad has done great research, and identified the 85 Norwegian mountains with a primary factor of more than 1000m. He has identified a number of mountains, far less known that Galdhøpiggen or Rondeslottet, but by no means less prominent. On his web page, you will also find links to other primary factor lists from around the world. Go and have a look. 

Back to my HORDALAND page

Back to my HOME page