Activation zone boundary annotation on maps

Is there somewhere on-line where one can view the Activation Zone (AZ) boundary for UK SOTA summits drawn on an OS Map [or equivalent]? Or does one need a special software tool / app to produce the annotation?

It’s not something you can work out by hand as contour lines are at 10m intervals. If say, the summit is at 159m ASL then the AZ boundary runs along the [unshown] 134m contour.

Until now it’s never been an issue for me because I’ve either activated at or close to the summit [usually the unpopular ones or early in the morning when nobody’s about] or within about 5-10m vertical drop from the summit. However, with social distancing being encouraged even after the current lockdown ends and with heightened awareness of EMF separation distances soon to be required by Ofcom, there will in future be some summits where I would want to locate closer to the AZ boundary.

73 Andy


The short answer - “no”.

I think in some places you might find 5-m contours. But I might be thinking of the 1:10k map series.

Unlike e.g. Spain there is not complete and publicly-available LIDAR coverage for GB. The next-best thing is the OSGB 5-m grid elevation model. But actually even LIDAR would not be the perfect answer, in case it is picking up any man-made features above the underlying ground surface. Only a site visit can answer this. The Terrain5 model certainly is not 100% reliable. Then again it’s as good as the resulting maps! (i.e. the contours aren’t perfectly reliable either, to be pedantic.)

Yes, I understand the issue in respect of social distancing. I don’t think it’s an issue wrt the EMF. Activators in other jurisdictions have operated under similar conditions for years. In any case perhaps there aren’t so very many G summits where the AZ is large enough to be able actually to hide away and not draw on-lookers as soon as you put up a pole! (Fortunately G/SP-001 is one!)

If you’d like to identify particular summits, at some effort (i.e. don’t ask for many!) I can try to help.

Oh, and some might suggest flooding on Google Earth. Fair enough, but I doubt it’s any better than eye-balling an interpolation between the contours - i,e, not really good enough when you want to get right to the limits.

Some of my OS 1:25k maps have 5m contours shown.

I raised a qustion about consumer grade GPS height accuracy in this thread: GPS height accuracy?
(good grief, is it really that long ago?)

It has occured to me since, that although the absolute height accuracy is not great, relative accuracy might be useful eg if you visit the summit and note the height reading on your GPS device, is it safe to assume that readings showing a difference down to 25m lower are reasonably accurate? You would of course have to keep in mind the other rules concerning intermediate cols etc.

This doesn’t answer Andy’s question, but it might be a practical solution when a visit to the summit doesn’t involve too much of a detour from your proposed activation place. I suppose that for most summits with a very large AZ, it wouldn’t be too hard to find a spot from the map anyway.


(I’ve just re-read the old thread, interesting stuff - there would still be a height uncertainty for the relative reading, I wouldn’t trust it to the nearest metre or two…? )

Modern smartphones – at least higher class models – have barometric pressure sensors with astounding relative accuracy (see e.g. Pressure Sensors Overview | Bosch Sensortec). Some dedicated handheld GPS devices might have them too.

In cases where the extent of the AZ is not clear, or the depth of a col/notch has to be determined, I like to use an app that can read the sensor, calibrate it to a known altitude at the summit, and then use the relative measurements. Of course it should be done in a fairly short amount of time after calibration, and perhaps repeated going the other way.

73, Manuel

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Hi Andy,
What you could use is Google Earth and the flooding feature. Set your flood level to 25 metres less than the summit height and you have the AZ border.

73 Ed.


Even better, why not just relax in a comfy armchair and enjoy poring over an OS Explorer 1:25000 map of the summit being planned?


But I’d be interested to know, if you just stand still for 5 or 10 minutes (~ time to walk to edge of AZ?) about how much do they change? Maybe then add an allowance for this?

Perhaps one day consumer grade GNSS will be good enough, but until phones have multi-band RX (do any?) we will be at the mercy of our friend, the ionosphere.

My watch (Suunto) combines GPS with barometric pressure measurements - and when provided with a reference seems very accurate - certainly over 10 mins and a short distance if it had been given a reference at the summit. I must admit I like Tom’s idea - and when playing fantasy activations in lockdown I use a combination of OS maps online and photos on google maps to give me an idea of the summit - all the popular ones where social distance is likely to be a problem have loads of summit photos. I am also thinking that for some lakes summits on HF a vertical might be much easier to manage than my usual linked dipole arragement. Fingers crossed that we will be able to put the theory into practice sooner rather than later. PS Must stop looking at The Reflector when I am working in the office…PPS Great Gable is still my preferred end of lockdown summit - but it could be popular and I think it would be one for a vertical or a very early start… Paul

I’ve just left my phone sitting on the desk for 15 minutes, and during that time, the reading has drifted around within ± 0.5 m of the initial reading. So probably not suitable for finding the very edge of the AZ down to the last metre :wink:


Pretty impressive.

Try it in outdoor varying temperature conditions though…?


It is not just the temprature but the metrological air pressure. An aircraft altimeter has a little knob on the side to correct for this. to range from 1050mb to about 930mb. At 10m/mb i.e. 1200m range. Practically the day to day range is more like 40mb or 400m. So a barometric altimeter can only be as accurate a its refrence at the time of the reading.

73 de

Andrew G4VFL

Isn’t that QNH or such?

QNH is based on regions (Altimeter Setting Region) the pressure setting is set so an aircraft flying in that region will clear the highest obstical in the region. Thus if you land at an airport your altimeter may not show the correct hight of that airport but will be pretty close. Hence landings are normally done with QFE which is given to the pilot by the airport, this allows the altimeter to show the hight above the runway. The airport could give you the QNH for the airport and you land based on altitude.

As far as the 25m below the summit is concernced I would trust a map, most summits are not too busy.

73 de

Andrew G4VFL

Are aircraft altimeters still using mb? I thought that hPa was the standard unit now, not that it matters since hPa=mb but its nice to conform on units.

Yes, why not - like Wainwright used to do Tom, night after night in the winter by the fireside…

You are right they changed from mb to hpa in 2011, I stopped flying before that. The USA still uses inches.

73 de

Andrew G4VFL

They would! :rofl:

… today the weather is very windy and the air pressure drops quickly.
I’ve left my phone on the desk for three hours and - according to the altimeter app - it seems my desk has gained 14 metres in altitude :wink:

But I agree, in stable wx conditions and within a short time frame (maybe about 10 minutes) the differential measurement should be accurate enough to find the edge of the AZ. Maybe not to the last metre but it’ll work with some margin.
73, Roman