EASILY determining Prominence of an area in question

The Reflector has been mostly quiet the for a few hours, so I thought this might be a good time to bring up a question about QUICKLY determining whether or not a specific spot (that looks very promising visually) actually has sufficient SOTA prominence to qualify as a Summit. I had a specific area in mind, and I have read that it is not uncommon for Association Managers to field questions about this. Someone is certain a particular spot just has to be a Summit and they want to know how to get it listed.

The area I had in mind is Mt. Penn, which overlooks (towers above it actually) Reading Pennsylvania. I thought that surly the W3 Association Manager must not be familiar with the area, and it somehow just got overlooked. Then I looked up the address for the Association Manager. It turns out that he actually lives in … (wait for it) … Reading Pennsylvania. Well, so much for that theory.

I contacted him anyway, and was basically advised that if I could demonstrate prominence, if verified it could be added. OK, how hard could it be? The high point of Mt. Penn is where the Fire Tower was built at a base elevation of 1120 feet at the coordinates of ( N 40.3467, W 75.9026 ). All I had to do was follow the 600 foot elevation contour line around that Tower, and I would be set (I do understand that would have slightly exceeded the actual prominence requirement). It turned out that contour line weaved its way through 5 counties, and eventually enclosed a slightly higher elevation point (a listed Summit) nearly 15 miles away. Wow. Is it unusual to determine the true Summit is that far away, and have slightly lower competing Summit candidates disqualified over that large an area?

I had my answer. It wasn’t exactly easy and after all that it was NOT a Summit. Is there anyone out there that could have come to that same conclusion much quicker and easier? Being able to introduce a custom sea level to an area at any elevation I choose would have instantly answered my question. I found discussions about “flooding” an area. But I could never figure out how to do it. That is a mapping tool I would like to experiment with.

This is probably just an academic question now. If SOTA already knew that Mt. Penn is not a Summit, I seriously doubt any place that has been equally analyzed will yield any more “hidden” gems. Has every association been equally analyzed?

Glenn –AB3TQ

Thanks for sharing your experience Glenn. That may be most helpful to people in getting to grips with topographical prominence. It is a robust concept, but not one that is universally easily understood.

I think most places already covered by SOTA have been analysed in this manner, which is why “finding new ones” is so rare. New summits in existing associations are more likely to be the result of updated elevation and saddle data produced by resurveying.

Surprisingly, no it is not. I have seen as much as 100km in some of the flat lands. Then when you get to finding the true col, in the case of GW/NW-001 the col or saddle is on the banks of the Forth Clyde canal in Scotland approximately 325km away.

Give an eye to this page:

This may help.


How To Identify Peaks and Saddles.

The map above contains three peaks all over 150m (A = 210m, B = 250m and C = 230m) but only two qualify for SOTA. The following maps will explain why.

The map above shows the saddle for peak A. To determine the saddle for peak A you start at the highest point and work your way down tracing around the contour lines until you get to the last contour line that totally in-circles the peak as shown above. The saddle is the lowest point (15m) making the prominence (195m).

Now if we look at peak B (250m) and peak C (230m) the saddle is around 110m making the prominence for peak B (140m) and peak C (120m). As peak C does not qualify, it now becomes a part of peak B so now we continue to trace the contour lines until you get to the last contour line that totally in-circles the peak as shown below.

The saddle is now the same as peak A (15m) and makes the prominence of peak B (235m).


Nice illustration! Maybe it could be added to the SOTA FAQ?

73 Richard G3CWI

it makes more sense went you can see it.

1 Like

The Google Earth “flooding” function kml file and full instructions on how to install are at Google Earth 'Flood'.

Instructions on how I used it when working on VK2/HU region are in the VK SOTA Yahoogroup files area.

73 Ed.

Nice illustration! Maybe it could be added to the SOTA FAQ?

What SOTA FAQ? There’s one on the opening page of the database, which is empty. Is there another? We’ve been invited to send pictures to adorn the home page of the database; why not invited us to send proposed Q & A’s for the FAQ page? You have to pick from among the photos, so would it take any more time to pick from among the Q & A proposals? About five of them are urgent, and you could add one a month. Volunteer editors are a dime a dozen, starting with me and K6DGW.

Elliott, K6EL
Eager Awaiter

While this explanation is adequate for assessing whether a summit qualifies for SOTA, what it identifies is the proximate col/saddle and not the true col/saddle. Prominence is defined relative to the next higher summit. So in the example above if there is somewhere on the same land mass, another summit with a height of 220m, the prominence of A will be defined relative to that summit and could well be a quite a distance away, well off this map. For example the prominence of Denali is defined relative to Aconcagua and the col/saddle at 56m is somewhere near the Panama canal, See List of mountain peaks by prominence - Wikipedia

Hello Glen
Not easy to validate a summit !
Here I use a free software : Landserf (http://www.landserf.org/)
Landserf works with many geographical data such as SRTM data from the NASA.
So you don’t have to buy maps, or go to and near the summit…
73 Alain F6ENO

I wrote a blog on how to install and use the Flood tool in Google Earth to map out SOTA activation zones. Hopefully it’s easy enough to follow along and use!


73 - Rob VK2GOM

Hi, Elliott, there is a large FAQ on the website - halfway along the menu bar of Sotawatch is the button that takes you to the website, and halfway along the menu bar of the website is the FAQ. This FAQ was laboriously compiled by me from about ten years worth of actual queries to the MT, I would hope that it covers all the more likely queries but it can be added to if anything new turns up!


There was a database FAQ but it got “regressed” away in an update. It’s due back soon!

Hi Glenn,

I’m sure every summit surveyor has their own preferences. I use an iterative process which has evolved.
Having located a candidate I go to a digital map and look at the 50 m contours. Some summits can be ruled out at this stage, others penciled in for the next stage. For what appears to be straight forward evaluations I go to a digital map published by the State or Federal government which have contour lines no more than 20 m apart plus reliable spot heights.

If I find an encircling contour that gives prominence then it is just a matter of stepping down the contours until a minima is found. In the past I have actually printed out several screen grabs to manually trace difficult contours.

Now in some places the contour lines go all over the place for tens of km. This is the stage where I go to Google Earth and using the polygon tool draw a rough rectangle or circle around the suspect peak. Flooding is applied starting with the peak just 5 m or so out of the water and dropping the level from there until a bridge to another peak is formed. Examination of the relative heights of the saddle and the peak will reveal if it is worth pursuing. The location of the saddle is found by centering it on the display and reading the co-ordinates off the bottom right of the screen.

Then the more reliable government digital map is used to check the height and firm up the position of the saddle. the spot height if available of the summit is then compared again to the saddle height and the summit is either in or out.

It is exciting when you stumble across a missed peak!


Very cool.
Just checked the massive extent of my local summit!

Useful tool :smile:

The separated bit showing green (top right) is not in the AZ… :wink:

Yep, you need to take the flood height down from the summit height metre by metre to see whether there are any dips that could affect the AZ, until you get to 25 vertical metres down but it’s real value is in confirming prominence of the hill overall.

By the way if when you expand the picture the lines go all blocky or part dissapear, that’s a performance issue, either on the (shared virtual) computer or on the network link between you and the server. If this happens, better to take a couple of hours break and then come back and try again.

73 Ed.

Hi Ed,

Google Earth flooding is a helpful indicator but goes awry when you have too large an area. I recently tried to use it with a coverage over 400 km and it gave incorrect results away from the centre. Why 400 km? Well looking at a new peak the nearest higher peak was 350 km away. It is important to get this one right or as right as can be done as then the surrounding peaks can be referenced to this one but even this comes down to some tedious eye-crossing contour tracing. Only a few peaks seem to have the ideal saddle disposition. In VK6 most contour lines look like a starfish that was crossed with a millipede and then suffered a terrible accident. Even finding the saddle to the nearest other qualifying peak can take many tedious hours. And then someone else has to double check.


Hi Ron,
Agreed Google Earth, especially when used in conjunction with SRTM data is not wholly accurate. I always checked my findings on a high resolution mapping site for NSW when I did the Hunter region work, to be “really sure”.

400Km accuracy on flooding? It doesn’t surprise me that this free tool complains at that. Unfortunately other tools that have a similar capability seem to cost hundreds of dollars which I, for one, cannot justify.

73 Ed.