UKC

I record my commute, try and vary it but end up doing basically the same routes again and again so I tend to know the mileage, and elevation of each route.

Noticed that in last week the mileagae and elevations have changed though - not by a lot but enough to be noticeable when it appears in the dashboard.

I have not changed my recording device  - just wondering if anyone else noticed this?

Is this due to one of the latest "upgrades" to strava, with them now trying to work out which device I am recording on so missing out the first section (looking at the map it would appear that the first section is missed on last few outings)

(I'm not bothered, just wondering, as its only out by half mile on each journey, and it is only commuting mikes, just an idle musing)

Received wisdom for these things is that there are a number of variables that affect the accuracy of your GPS receiver. The thing is, you don't know which reading is right anyway.  For example, I recall someone wondering how Trafalgar Square could be below sea level according to their GPS.

Point to point interpolation might effect total distance readings. Since the upgrade are all the setting still the same for recording rate? One issue I sometimes have is that my Wahoo Element Bolt takes different amount of time to get a lock when I set off. I can on occasion go quarter of a mile before it starts recording.

It's why Nelson's on his plinth. And the Strand used to be a beach.

What device are you using ? What I have noticed is that they tend to be less accurate on wet and cloudy days - takes longer to find a satellite and the elevation changes in particular are often quite inaccurate.

For added fun you can try recording the same ride both on a device like a Garmin, and on the strava app on your phone, and then spend hours trying to work out which is the more accurate. Or flattering to your ego. Seriously, you can lose days doing this!

Not noticed anything with my Strava recordings lately - commuting miles all seem pretty identical.

Years ago, I managed to log an altitude gain of about 400m while out with the running club - on a flat track session! Apparently a one-off - it hadn't done it before or since. Sent the data to Timex, but never heard anything back.

It's never completely accurate. I've done identical activities with friends and we've all recorded different distances and altitudes.

One thing I've noticed recently is that my Garmin takes a lot less time to find satellites and is much more sensitive to when I start moving (although I'm sure this is not related to Strava)

Man with one GPS knows where he is, man with two GPS never quite sure

When my wife and I go out together on our bikes, she with an iPhone, me with a Garmin, she consistently gets awarded 3-5% more distance and elevation, but only about 60% the calories. This irks her no end. However, from what I have read in papers, her phone seems the more likely to be nearer the truth on that.

A Strava glitch I get every week or so now is that I add a run and my annual miles total goes down. I can refresh my stats, and I may get back to where I was, but it takes a few days until, at some random moment, my correct total (I think) reappears. The fantastic Veloviewer site seems to keep a correct track of things.

That's why they built the Thames Barrier, isn't it?

I think sea level is not necessarily at the level of the very highest tides.  Certainly, Trafalgar Square is higher than that, but I do remember, as a child, lots of very wet pavements and stepping over the big baulks of timber that used to be installed at the entrance to Embankment tube.  I've always taken sea level in London to be normal high tide.  Might be wrong though.

In terms of sea level in the UK (and mapped heights generally), everything is related to Ordnance Datum (OD).

OD is usually taken as mean sea level at Newlyn in Cornwall, which is itself defined as the average tide height over a period of time at that location (i.e. over a number of years, although I cant remember which ones). 

Tide heights in London and elsewhere in the UK will obviously vary from this due to local hydrology and tidally effects, so Sea Level/OD used on UK maps is not necessarily the mean sea level at all locations. 

Not really sure how all this relates to use of GPS data, I guess there will be a lot of automated correction and smoothing of data involved, to relate GPS recorded heights back to OD?

On the topic of tracking anomalies, what's to be made of this one?

https://www.strava.com/activities/1811002899

A gentle riverside run in the Val d'Ayas last month shows an entirely fictitious deviation several hundred feet up the hillside and a precipitous descent through dense forest.

Garmin 235, seen nothing like it in the couple of years I've had it.