Your GPS Is Wrong and the Guidebook is Right

[andycohn]

At least 2 - 3 times a week, I read a post where someone complains that the guidebook s/he’s using (Brierley is most often singled out for the blame) understates the distance actually walked, as measured by the poster’s supposedly reliable gps. And in fact, since my wife started carrying a gps measuring device several caminos ago, we’ve noticed the same thing — that the guidebook, app. or website we’re using generally understates the gps distance by 5 - 10%.

BUT (we’ve also noticed), it doesn’t matter what guidebook or app we’re using — Brierley, Wise Pilgrim, Gronze, Whitson, CSJ, or others in different countries — and it also doesn't matter which of several gps devices my wife is carrying. The gps distance is always greater than the distance stated in the guidebook or app.

So can all the different guidebooks be wrong, and all the different gps devices be right?

The answer, obviously, is “no,” and if you do a simple google search for “Accuracy of GPS distance measurements,” you’ll find a ton of information, including from gps manufacturers like Garmin, which all acknowledges that gps measurements always overstate diistance by a factor of 5% or more because of the limitations of the technology. As I understand it, the reason is that gps devices measure distances not in the continuous line you are walking, but from various fixed points, all of which are several meters or more away from the actual point you are walking, so when all the gps dots are connected up, the total distance shown will be greater than the distance you actually walked (kind of like measuring the legs of the triangle instead of the hypotenuse). Here’s a good, clear article that explains it: http://cincyhalfmarathon.com/GPS Accuracy.pdf

So what’s the lesson here? Put your phone down, and walk! You’re going to get there when you get there. Easy to say, I know.

 

[Bradypus]

There are times when pinpoint accuracy is vital but I doubt if that often applies on the Caminos. My father-in-law used to work on the software side of navigation systems. One of the company's engineers was sent to investigate an error a customer reported on a boat's gps systems. Two receivers consistently reporting different positions - out by about 10 metres. The gps engineer asked where the antenna for set A was mounted. "Port side of the bridge". And set B? - "starboard side". He then asked the ship's engineer what the beam of the boat was. "About 30 feet". Mystery solved

 

[naplesdon]

No big deal, we are talking about the difference of steps between the bar and the albergue, n'est pas?

 

[RJM]

The guidebooks are all reasonably accurate enough in distances.
For the most part on the Frances (the most popular) if the book is off a bit, what difference would it make anyway? You can see your destinations in the distance. At that point why would one still be concerned? Just keep on walking.

 

[t2andreo]

The best GPS measurements for the Camino or any hiking route are those taken at ground level using many waypoints. Few guidebooks are done this way.

However, I can tell you that the Wise Pilgrim series of guidebooks and apps were developed, and are updated regularly, using a GPS unit mounted on the author's bicycle. Many, en-route waypoints are used. I am not certain of the frequency, but I believe the author has his GPS set to mark a waypoint at regular, timed intervals. This results in a very accurate 'dotted line.' I will let @wisepilgrim chime in here...

The resulting additive distances from one town to the next are much more accurate than periodic or point to point GPS measurements taken. That is why the Wise Pilgrim distances are frequently at variance with other guidebooks.

In addition, and in a related matter, some years ago (about three, I think) someone in the Cathedral hierarchy had all the distances used at the Pilgrim Office to determine the 'official' distance for formal pilgrimage purposes recalibrated using GPS technology. That is why Saint Jean Pied de Port went from being 775 km from the Cathedral at Santiago, to 799 (NOT 800) away.

Evidently, the previous 'official' distances had been determined decades ago using a mechanical surveyor's wheel propelled by a walking pilgrim. I know that these distances can be very inaccurate especially over multi-km distances. The surveyor's wheel is mechanical and subject to the inaccuracy inherent in manual / analog pedometers and other, similar measuring devices.

I have been informed that using GPS from church steps to church steps, from town to town along the way, was the official (Church) methodology. The Brierley measurements ar from albergue to albergue.

Also, BTW, the OFFICIAL distance marker at Santiago is NOT the Cathedral, per se. It is a plaque set in the exact center of Plaza Obradoiro, in front of the west facade of the Cathedral.

Most major world cities have a similar distance marker, from which all official distances are measured and determined. For example, in Washington, DC it is a bronze marker set in the Ellipse, between the White House and Washington Memorial. In New York City, I believe it is the center of Times Square. Your capital city, and other major cities: e.g. London, Paris, Sydney, Lisbon, Madrid, Rome, Tokyo, Buenos Aires, etc. likely have a similar point.

Hope this helps.

 

[Dave]

The best GPS measurements for the Camino or any hiking route are those taken at ground level using many waypoints. Few guidebooks are done this way.

Man, is that true? I've often wondered, as I slog through the inland approach from Laredo to Güemes, again, if other guidebook writers are going back through every route in their book, too. I understand the temptation in particular in the age of abundant gpx tracks online. But in our case, every route is recorded via gpx with tons of track points, and then manually tidied up afterward (the tracks are never clean in densely wooded areas). I have tweaked probably a quarter of the track points on each recorded track by the time I'm done polishing. It's tedious, but all of the info that follows builds out of it. It's a bummer to think that some guidebook publishers are callous enough to take shortcuts on that.

 

[KinkyOne]

Well, I really don't know much about GPS technology and I'm using my smart phone for track recording but I found distances measured by Wikiloc pretty much the same as Brierley (talking about Frances), while Endomondo gave me 5-10% longer distances.
BUT nobody here mentioned one other very important fact - from where to where the distances in guidebooks are/were measured??? Even with Wikiloc I found out (on other Caminos) that more or less guides have village-village (the marker for end and start of the settlement) and not albergue-albergue or plaza mayor-plaza mayor distances. In case of just a bit bigger towns that can add up to 5-10km!
For example the CSJ guide for Madrid has one of the last stages waaay too long. Thanks to that I had beautiful experience in Grajal de Campos because I pushed on from the planned stage
Regarding this I found out that Brierley is the most accurate of them all that I have used.

 

[Dave]

BUT nobody here mentioned one other very important fact - from where to where the distances in guidebooks are/were measured???

It's especially huge on the Norte, where some towns--San Sebastián, Bilbao, and Gijón first and foremost--are so dang long and albergue options so spread out that you can have many extra kms waiting you. I wrote this once about distances on the first stage of the Norte:

With so many places to start this stage and so many to finish, it can be really tricky to gauge distances. Here are a handful of different ways to calculate:

Part 1 - From ________ to Santuario de Guadalupe
a) From Irún albergue: 4.5km
b) From French border: 7.3km
c) From Hondarribia port: 4.9km

Part 2 - From SdeG to Pasajes
a) Following the suggested route (Alpinist/Camino): 10.5km
b) Following the low-level variant: 11.7km
c) Following the coastal variant from Hondarribia: 24.5km
d) Following the Alpinist route + the GR: 11.8km

Part 3 - From Pasajes to Hospital de Peregrinos Claret Ikastola in San Sebastián
a) Following the suggested route (Camino): 6.4km
b) Following the Camino + GR: 7.3km

Continuing to arrive at Albergue La Sirena in San Sebastián +3.9km

So, depending upon what you choose, the day's distance can vary quite a bit!

 

[KinkyOne]

...
Continuing to arrive at Albergue La Sirena in San Sebastián +3.9km

So, depending upon what you choose, the day's distance can vary quite a bit!

Exactly! And walking through town 3,9km can easily extend to 1 hour

 

[Telboyo]

If you have a TomTom runner or even a cheap chines copy they will both give you an extra km per day if you brush your teeth whilst wearing them. They are usually about 10 per cent out unless you select the freestyle option and leave it on for an hour. When you look at your TomTom at the end of the day the figures will differ with those on the app after you download a d sync it.

 

[Jeff Crawley]

If you have a TomTom runner or even a cheap chines copy they will both give you an extra km per day if you brush your teeth whilst wearing them. They are usually about 10 per cent out unless you select the freestyle option and leave it on for an hour. When you look at your TomTom at the end of the day the figures will differ with those on the app after you download a d sync it.

If I forget to take off my FitBit-alike (right wrist) when I'm at ukulele group I clock up a good 4500 extra steps in two hours - no wonder I feel better when I leave.

 

[Jeff Crawley]

Consider this: SJPP is where it's always been; SdC is where it's always been.

The length of the route you take between the two points depends on several variable and varients but, when it comes down to it, unless you're commanding a precision cruise missile strike (which is what the US GPS system was built for) does it really matter if you expected to walk about 14.5km and ended up walking 14.892km?

 

[dougfitz]

I am having difficulty taking any of this very seriously. I thought that it was pretty obvious why GPS measurements of the camino were longer than those stated in any guidebooks. Every time you stop for a coffee, your GPS is going around having a chat to all the other GPSs, and puts up a whole lot of extra distance while you are having a rest!

 

[Jeff Crawley]

GPS receivers are like exuberant puppies - unless you keep them on a tight leash they'll be all over the place:


That's 585m rather than the straight line distance of 180!

 

[andycohn]

Man, is that true? I've often wondered, as I slog through the inland approach from Laredo to Güemes, again, if other guidebook writers are going back through every route in their book, too. I understand the temptation in particular in the age of abundant gpx tracks online. But in our case, every route is recorded via gpx with tons of track points, and then manually tidied up afterward (the tracks are never clean in densely wooded areas). I have tweaked probably a quarter of the track points on each recorded track by the time I'm done polishing. It's tedious, but all of the info that follows builds out of it. It's a bummer to think that some guidebook publishers are callous enough to take shortcuts on that.

Hi Dave: Wasn’t meaning to criticize you and the other wonderful guidebook writers, but to make a little fun of the rest of us, who put our naive faith in an imperfect technology and then get so self-righteous about the supposedly wrong guidebook writers who work so hard — like yourself — to get it right.

 

[Dave]

Hi Dave: Wasn’t meaning to criticize you and the other wonderful guidebook writers, but to make a little fun of the rest of us, who put our naive faith in an imperfect technology and then get so self-righteous about the supposedly wrong guidebook writers who work so hard — like yourself — to get it right.

Sorry to be unclear, Andy! I was replying to Tom's comment in that post, not yours. And no offense taken at all. I have been on both sides of this fence, ruefully shaking my fist at a guidebook when it feels like the distances are off, and also receiving emails and reviews that question our accuracy, credibility, and motives. It comes with the territory. And, on occasion, we screw up and it's deserved, and it sucks to know that you made someone's day worse with bad info.

I just wondered about Tom's point about the commonality of this practice.

 

[jungleboy]

Interesting discussion, thanks for starting it.

At least 2 - 3 times a week, I read a post where someone complains that the guidebook s/he’s using (Brierley is usually faulted for the blame) understates the distance actually walked, as measured by the poster’s supposedly reliable gps.

Interestingly, I’m experiencing the opposite on the Camino de Madrid right now. The in-built iPhone Health app is consistently understating the guidebook / Gronze distances by 10-15 percent.

For example the CSJ guide for Madrid has one of the last stages waaay too long. Thanks to that I had beautiful experience in Grajal de Campos because I pushed on from the planned stage

Good to know as I have that book and will reach that stage later this week. We’ve been told that the albergue in Santervás de Campos is closed at the moment so we were thinking of going to Grajal anyway.

 

[andycohn]

Sorry to be unclear, Andy! I was replying to Tom's comment in that post, not yours. And no offense taken at all. I have been on both sides of this fence, ruefully shaking my fist at a guidebook when it feels like the distances are off, and also receiving emails and reviews that question our accuracy, credibility, and motives. It comes with the territory. And, on occasion, we screw up and it's deserved, and it sucks to know that you made someone's day worse with bad info.

I just wondered about Tom's point about the commonality of this practice.

Not unclear at all. I also wondered about the “commonality of this practice” (i.e. slipshod measurements). Personally, I’m skeptical when laymen like most of us question the responsible professionals (like you and Brierley and Wise Pilgrim) who create our guidebooks. Unless you’re a professional yourself, with professional equipment, how can you possibly know that someone else’s measurements are wrong?

 

[naplesdon]

I found one problem last year.
Does your device measuring the distance traveled by constantly following your route location by GPS or is it measuring the distance like a pedometer. Like most health apps, if it tracking your walking pace you need to do some serious calibrations. In my case my average pace is not one meter, is about 60% of that and if I am climbing mountains or traveling across rocky terrains, forget the calibration.

 

[KinkyOne]

Whenever I stopped for a bit longer break to have a beer or two I stop my GPS tracking recorder. But I think the main problem in this discrepancy is availability of satellites at certain moment. At least three needed as I've heard. The more the merrier

But for example when I look at my Endomondo GPS track very closely it's a total zig-zag whereas the Wikiloc has straight line. On the same Camino and same very straight stretch! And Endomondo has 5-10% longer distances. Why is that? Software? Anyone knows maybe?

 

[Jeff Crawley]

Whenever I stopped for a bit longer break to have a beer or two I stop my GPS tracking recorder. But I think the main problem in this discrepancy is availability of satellites at certain moment. At least three needed as I've heard. The more the merrier

But for example when I look at my Endomondo GPS track very closely it's a total zig-zag whereas the Wikiloc has straight line. On the same Camino and same very straight stretch! And Endomondo has 5-10% longer distances. Why is that? Software? Anyone knows maybe?

It could be to do with the intervals between samples - if you've set your GPSr to record say 5 minute intervals how far have you traveled? Have you jinked left or right ot gone straight? Also some GPSr are limited in the number of points they record so they may have a reduced level of accuracy.
I have noticed that tracks loaded onto Wikiloc can be different to the same track loaded onto Viewranger.
Does it cause a huge problem? Probably not.

 

[dougfitz]

Unless you’re a professional yourself, with professional equipment, how can you possibly know that someone else’s measurements are wrong?

I also wondered about @t2andreo's post here. Certainly GPS is not used by the IAAF and national athletics associations for any official distance measurements. Leaving field measurements aside, longer track measures are normally done using a suitable bicycle fitted with a 'Jones counter' (http://www.jonescounter.com/ ) and the measurement procedures are well defined (see here for the USTAF online procedures manual http://www.rrtc.net/procedures_manual/Procedures-Manual.html ). Suggesting these techniques have a similar level of accuracy to a pedometer makes no sense to me. They are expected to achieve accuracies of better than 1/10 of 1% in distance or 1 part in 1000 - about 42 m for the marathon. Add to that there is a short course protection factor to ensure that no course is less than the certified length to avoid challenges on this count when records are claimed.

My previous comment was only half in jest. If you are stationary, the GPS will continue to take measurements subject to all the inaccuracies of the system. It will appear to wander around, as @Jeff Crawley's post capably illustrates. The distance it wanders will increase the longer you linger over coffee. For my 2016 camino, when I extracted all these, the total was over sixty kilometres - about three days walking.

I doubt any well informed GPS user on this forum would find that unusual, so I found the OP's assertion that this is a regular theme on this forum surprised me a little. I did think that might have been literary hyperbole! I did read the article at the link in the OP, and it is far from clear and certainly far from completely accurate. A simple and completely accurate statement on the matter can be found on the USA Track and Field website here http://www.usatf.org/Products-/-Ser...r-Course/Statement-on-GPS-Use-by-Runners.aspx .

 

[dougfitz]

Does your device measuring the distance traveled by constantly following your route location by GPS or is it measuring the distance like a pedometer. Like most health apps, if it tracking your walking pace you need to do some serious calibrations. In my case my average pace is not one meter, is about 60% of that and if I am climbing mountains or traveling across rocky terrains, forget the calibration.

You are absolutely right on this. Distance estimates based on step counts are always going to be vexed. While I doubt that you mince along at 60 cm a step normally, it is equally unlikely that anyone except the very tallest people would have a pace length of a metre. I estimate that mine is about 82 cm on the flat, but even that can vary. At that rate it would take about 12000 steps to cover 10 km, but when I am out bush-walking, that distance (measured on my inherently inaccurate GPS!) might take anything up to 15000 steps, or an equivalent step length under 70 cm.

I no longer set my daily exercise targets as distance, but use step counts and stair counts instead.

 

[naplesdon]

Yeah, when you agree with me I feel like I have won a debate!!!!

 

[Camino Chrissy]

I have walked four different caminos and leave in a week for a fifth. I am quite techy challenged, but I just walk and get a general idea from my trusty guide book and maybe an app as to how far I will be walking on any given day and the basic elevation profile so I have an "idea" what I am in for. We can not predict the weather with accuracy, so why do we worry about each step we take...it has always worked out for me and it will for all of you, too! No probs!

 

[mark connolly]

I have been informed that using GPS from church steps to church steps, from town to town along the way, was the official methodology.

Also, BTW, the OFFICIAL distance marker at Santiago is NOT the Cathedral, per se. It is a plaque set in the exact center of Plaza Obradoiro, in front of the west facade of the Cathedral.

Most major world cities have a similar distance marker, from which all official distances are measured and determined. For example, in Washington, DC it is a bronze marker set in the Ellipse, between the White House and Washington Memorial. In New York City, I believe it is the center of Times Square. Your capital city, and other major cities: e.g. London, Paris, Sydney, Lisbon, Madrid, Rome, Tokyo, Buenos Aires, etc. likely have a similar point.

As far as Brieley's book in concerned, referencing the above quote, his distances, I believe, are not measured from the center of cities/towns or catherdrals/churches. They are measured from the last alburgue in the city/town to the first alburgue in the next city/town. This is where the confussion is, I believe. He devotes a whole paragragh in the beginning of his guidebook about this. Since that info is at the beginning, most pilgrims probably just skip over this part. Bear in mind, I do not have Brierley's book in front me to confirm this. But I remember there was a passage stating how the distances are measured, etc.

Mark

 

[t2andreo]

I don’t think I addressed how Mr. Brierley derived his distances. In my post, I specifically explained how the new, official distances were measured.

Using GPS, distances were measured from the front of the main church in one town, to the main church in the next town. This followed the original methodology used in the original distance measurements going back many decades.

Originally, manual measurement methods were used. These analog measurements were more subject to error over distance.

Hope this clarifies.

 

[dougfitz]

They are measured from the last alburgue in the city/town to the first alburgue in the next city/town.

Not quite. If the distance is given it is to a particular albergue, it then starts from that albergue on the next map / stage. In my edition, it is clear which albergue is being used for the measurement of distance on the map and in the text. Where there are other albergues, these are either shown on the stage map or perhaps on a detailed map.

Originally, manual measurement methods were used. These analog measurements were more subject to error over distance.

@t2andreo, I don't think that normal handheld or vehicle GPS units have reached the level of accuracy where this is a reasonable statement to make. It might be true of survey quality GPS units which use a variety of measures to improve their accuracy, but certainly isn't going to be true for smartphones, GPS sports watches or even dedicated handheld or vehicle mounted devices.

I am speculating, but John Brierley was a surveyor, and it would be reasonable to presume he would have known how to access the high quality geospatial information needed to provide accurate distance and elevation gain information in his guidebooks.

 

[t2andreo]

Okay, I stand corrected, in part.

I defer to Mr. Brierley's expertise, subject to equipment and methodology limitations.

 

[Camino Chrissy]

You are absolutely right on this. Distance estimates based on step counts are always going to be vexed. While I doubt that you mince along at 60 cm a step normally, it is equally unlikely that anyone except the very tallest people would have a pace length of a metre. I estimate that mine is about 82 cm on the flat, but even that can vary. At that rate it would take about 12000 steps to cover 10 km, but when I am out bush-walking, that distance (measured on my inherently inaccurate GPS!) might take anything up to 15000 steps, or an equivalent step length under 70 cm.

I no longer set my daily exercise targets as distance, but use step counts and stair counts instead.

I know...Dougy can be a hard nut to crack!

 

[t2andreo]

Oh we get on just fine. We, sometimes just disagree on finer points.

Generally, we are on the same song sheet. It is never a problem for me. I accept that others may know more than me on any given subject.

I accept all charitable corrections. His are.

 

[Rick of Rick and Peg]

My previous comment was only half in jest. If you are stationary, the GPS will continue to take measurements subject to all the inaccuracies of the system. It will appear to wander around, as @Jeff Crawley's post capably illustrates. The distance it wanders will increase the longer you linger over coffee. For my 2016 camino, when I extracted all these, the total was over sixty kilometres - about three days walking.

As an example, last week I noticed a crack in the back of my smartphone and then noticed that I was not able to get a gps signal (I was out in the middle of a forest.) Later, once in town, I tried again and got a position a few blocks away from the street signs near me. As I watched I could see my location jumping around a few blocks at a time. If I had tracking on it would have had me putting in kilometers while I was standing still.

In my case I still was not getting signals from gps satellites so the app was using cell towers to estimate where I was. In the ideal situation where I would be getting satellite signals the jumps might have been maybe centimeters. But 100 of them would have added up to an extra meter of distance on a track.