Innacurate position recording

I have had Arc for two days with iPhone 12 Pro Max. On day one I made a drive to a place about 15 miles away but none of the journey was recorded although the destination did feature. On both days, it recorded me making lots of car journeys around the vicinity of the house which I did not do and also recorded a long string of different locations towards the south-east which I never went to. Any idea why these errors are occurring? I have Location set to Always and Background App Refresh turned on.

Try restarting your phone. Was the app running (not swipe closed) during the trips?

1 Like

Sometimes one or both of Arc and Arc Mini are running and sometimes they are not.

Today, for example, neither app has been open and I have not moved from the house and garden. For some reason, both apps show that I have been in a long string of different positions heading in a straight line up to 1000m east of my actual location. These are all within a blue circle which appears

Yesterday there were three similar straight strings in different areas up to 4,000m from where I have actually been. In addition a car journey I made of about 10,000m does not show at all nor any time I spent at that destination.

It seems either that my phone is giving odd data to Arc or that Arc is not able to collect data from my phone. Any help appreciated as I would really like to get it to work.

Hi @ajlholt!

It sounds like there’s a few different things going on there.

On day one I made a drive to a place about 15 miles away but none of the journey was recorded although the destination did feature.

For this, as @more said, firstly make sure you’re not swiping the app closed. And if it’s happening a lot, then it can be worth restarting your phone, in case iOS has got itself confused.

The next step is to install Arc Mini, as a fallback recorder, in case of Arc App getting killed off unexpectedly. With both Arc App and Arc Mini installed, they will share the recording task, with one picking up where the other left off, if one is terminated. There’s effectively no extra battery use, and it reduces the risk of data gaps considerably.

Ok, next up, messy location data:

Location data recorded by smartphones can be very noisy and messy. Both Arc App and the phone itself have ways of correcting for this and improving the accuracy over time. So typically the data is messiest the first time you visit a new place, and will improve quickly from then on.

  1. The phone itself makes use of wifi hotspot triangulation to improve its accuracy when indoors or when in built up city areas. This is done automatically, and you typically will see much better results within a day or so.

  2. Arc App then has another system on top - called Trust Factor - which makes use of your feedback (corrections of stationary data) to learn locations where the data is consistently untrustworthy.

    • To use this system, go into those nonsense segments or items, tap on the segments that have been classified as “car” or “airplane” or whatever other nonsense, and correct them to “stationary” (assuming you were stationary at the time).
    • Arc uses that feedback to learn how much the location data drifts about at that place, and corrects for that drift in future.
  3. However if the recorded data is more than about 100 metres away from the real location, that amount of drift can’t be automatically dealt with by the Trust Factor system, because it can’t be distinguished from real data (eg walking around the block). So in those cases, instead of correcting the drifting segments to “stationary”, mark them as “bogus”. Marking a segment as bogus will remove it from the map, and from the containing timeline item, cleaning up the mess.

I hope that help to explain!

Ugh. Yeah, this sounds like a case for using the “bogus” classification. That amount of drift is far too much for Arc to be able to clean up automatically using its Trust Factor system. The only way around it is to go in and mark the nonsense as bogus data, effectively removing it from the timeline.

That amount of drift usually only occurs when the phone doesn’t have enough wifi hotspot triangulation data at that place, either because it can’t see enough nearby hotspots or because it’s the first time the phone has been there.

Though it can also occur repeatedly at the same place, even when there should be enough wifi hotspot triangulation data available. In that case it’s an iOS bug, and one that used to be much more common a couple of years back.

I have seen that particular excessive data drift happening on my phone running iOS 16 beta lately. It does sometimes happen during iOS betas, presumably because Apple are flushing their wifi triangulation database at their end. In those cases, it typically clears up before the iOS beta goes final and live to the public.

Thanks for the replies and I really want Arc to work.

  1. I had already seen the benefit of installing Arc Mini which I had already done but are you saying that I need to have both apps actually open all the time in order for them to work even if I have location set to Always for both?

  2. How do I mark the locations as bogus? This will take a long time as there are so many points showing - all of which it thinks I made car journeys to.

  3. Why did it not record a 10km journey made yesterday nor an hour spent at that location nor an hour spent about 1km further back towards home?

  4. What is the large blue circle showing around my location?

  5. I can see from photos I take that the phone seems to know its position accurately so why is Arc not able to get that data from the phone?

Happy to send a screen shot if that can be done.


Definitely don’t swipe either of them closed! You can add Arc Mini’s “Current Item” widget to one of your home views, to be able to check whether both apps are still alive in the background or not. The little green/red dots at the bottom right of the widget indicate each app’s status (green = alive, red = terminated). So as long as you see two little green dots on the widget, you’re good to go and there really shouldn’t be any data gaps.

From the “Individual Segments” view, tap on a segment, then for “stationary” segments you can directly choose “bogus location data” from the menu, or for moving type segments you can tap the rubbish bin icon (which will then ask you to confirm that it’s bogus data).

I’ve been doing this a lot lately, due to iOS 16 beta causing quite a mess in my data. For “stationary” segments I typically tap on the segment in the list, then choose “not stationary”. That then shows me the segment on the map, so I can be sure I’ve picked the right one. Then from there I tap the rubbish bin icon to get rid of it. Or sometimes if I’m being especially pedantic I’ll tap the Split button, because only part of it is worthy of being marked as bogus.

But yeah, that process can be especially tedious if the phone is producing a lot of bogus data (as my phone is right now, with these iOS 16 betas!). And really if the phone is producing a lot of data that’s more than about 100 metres from the real location, something isn’t working right - the phone’s location services are failing in some way. It really shouldn’t be happening.

There’s two possibilities there: 1) both Arc App and Arc Mini had been terminated, so neither was alive to record the data, or 2) the phone had lost its grip on reality for a while, and needed to be restarted.

In the latter case, again that’s something that really shouldn’t be happening, and if you’re feeling especially pedantic and confident in identifying what’s happening, you could contact Apple about it. They’re the only ones who can fix that. Though contacting Apple Support isn’t likely to achieve anything useful in terms of getting the problem fixed in iOS, so it’s a bit of a lost cause. Just have to hope that it doesn’t happen frequently.

Is it light / sky blue, or more a purple blue? If it’s sky blue, then that’s the circle indicating the phone’s idea of where you are right at that moment, and the size of the circle indicates the determined accuracy of that data. So what it’s saying is “right at this moment, you are somewhere within this large blue circle”.

A light/sky blue circle with radius more than about 100 metres indicates the phone is struggling to even do sensible wifi hotspot triangulation, and is relying at least partially on cell tower triangulation, which isn’t great.

For the purple circles, those indicate Arc timeline items. If it’s on the map on the main timeline view, then it indicates a Visit, which will then have individual segments inside it, which you can view by tapping through to the Visit’s details view. If it’s on the map on a details view, then it indicates a segment within the visit (or trip).

A particularly large purple circle could indicate that there’s actually a series of samples inside the segment that could be changed to a moving type. For example a portion of a car trip has been incorrectly been classified as “stationary”. In that case, you can tap on the segment (or the circle’s dot on the map) and choose “not stationary”. Then you can see what it would look like as a moving type. It might turn out that it’s actually the lost car trip, and can be changed to “car” instead!

This is a particularly frustrating detail of the iOS bug where sometimes it loses its grip on reality. What actually happens is iOS stops providing location data to some apps, not all apps. So one app might still be receiving sensible location data, while another is being given nothing at all.

Arc has a built in way of detecting that case - where iOS has stopped sending it location data - and tries to snap out of it. Which sometimes works, but not always. Which is why you’re left with the only option being restarting the phone. Really not ideal!

Thankfully the worst of these problems have become much more rare over the years. But they do still crop up now and again, and sometimes mysteriously hit some people far more often than others. Why that is though… that’s a mystery.

Hi Matt

Thanks for the earlier replies.

Why do the apps actually need to be open on the phone if they are set to know my location at all times?

Why is the actual position that Arcs show me to be so inaccurate (meaning that the apps often think I must have jumped in a car and driven somewhere when I have not moved)? Why are the apps not as accurate as Photos (which always knows exactly where I am) and all the other navigation apps I might use such as google, apple, OS maps, etc which also don’t jump around?

Why do Arcs not update their position more frequently? I recently made a road trip from Dorset London and then travelled around London by various means and yet very little of it showed up at the end of the day. Other times I have flown somewhere and Arcs do not seem to have noticed that I have arrived till the next day despite being open.

I would happily do a lifetime subscription to Arc if it worked better!



The permission you grant is only that - a permission. When an app is not “running” it is not alive. It is a dead corpse. It cannot think, or move, or do anything at all. An app needs to be alive, or “running” in computer speak, to perform any action at all.

Arc has the permission to access location data at any time, but it must be alive to do that. If you swipe an app closed - any app at all - it can’t do anything until it is restarted. When Arc is swiped closed, it cannot record any location data until it is restarted. That’s just how computers work.

Arc is always more accurate than the Photos app. Arc requests the highest location data accuracy the device is capable of.

Arc will always request, and record, the highest possible accuracy your phone is capable of at the time. The difference between Arc and most of the other apps you mention is Arc is recording 24/7 while the others are only recording for short periods of time. If those other apps were recording at the same time as Arc when Arc is given bad location data, those apps would also show bad location data.

Those other apps don’t contain any magic - they are all simply relying on the location data that your phone produces. None of them produce their own location data - each app does not contain its own GPS antenna. They simply request location data from the phone, at a desired level of accuracy (Arc requests the highest level), and then make use of what they are given.

As I said above, Arc needs to be alive (“running”) in order to record any data. If the app has been swiped closed, or terminated automatically by the phone, then it will record nothing, and there’s no way around that. It’s how computers work.

Make sure that Arc is still alive, when you are doing things that you absolutely don’t want missed.

You can make this easier by adding Arc’s Current Item widget to your Home Screen. The widget has little green/red dots at the bottom right, which indicate at a glance whether the app is still alive or not. There will be one dot if you only have Arc App installed, and two dots if you have both Arc App and Arc Mini installed.

Arc App and Arc Mini share the recording task, so that when both apps are alive only one needs to be recording, while the other will wait in standby. If one of the apps is then terminated, the other app will notice this change and will take over the recording job, to reduce the risk of gaps in the data and timeline.

There is no other app that does this job as well as Arc. Arc has the highest accuracy and detail of all location/timeline recording apps on iPhone.

I am constantly working to improve Arc, making use of the greater abilities of newer phone models and iOS versions. But Arc is competing against itself - there is no competitor that equals or betters it.

I am happy to assist with problems, to help you get the most out of the app. But it should be made clear: you are not going to get better results from any other app.