How accurate is the mile calculation between GPS points?

[JDeJong]

I have GPS traces from a vehicles on the road.  How accurate is the spatial calc to actual driven miles on the road? 

Can I trust it?

[BrandonB]

Drive time and drive distance use TomTom data and the guzzler engine behind the scenes. You can read more about the process here https://community.alteryx.com/t5/Location-Data/What-Drives-Drivetimes/ta-p/17930 and here https://help.alteryx.com/current/designer/distance-tool for methodologies.

[JDeJong]

I don't believe the distance tool is accurate.  How can I be sure?

[BrandonB]

It uses TomTom data to take road data into consideration which people use all over the world for navigational purposes. Is there a reason that you aren't confident in the distance calculation? The distance calculation could be leveraging a different route than a driver took if you are looking at a comparison between the two. It also leverages traffic patterns so the options selected impact the drive distance and time. 

[JDeJong]

How is it using TomTom data?  I do not have the Location package.  

The route I have has lat/long for every five minutes of driving.  Somehow when I group by days and sequence by timestamp I get upwards of 1200, even 8000 miles.  In one day.   

[OllieClarke · Accepted solution]

@JDeJong might not be worth saying, but if you don't have the drive time/distance add on which @BrandonB is talking about, then the Distance tool will calculate everything as the crow flies (i.e. a 'straight' line)

[JDeJong]

Definitely worth saying!!  Thank you!!

[OllieClarke]

@JDeJong  could you share your workflow (and some date too if possible). The distance tool does accurately output distance (even in straight line mode), so there might be something else going on.

[BrandonB]

This could just be the way that it is configured. Have you validated that the lat/long are being properly turned into the spatial points that you would expect? Can you add a browse tool after the create points tool to visually check if all of your points are reflected properly? Also, the distance tool is looking at the distance from one point to another, so it sounds like you are looking to find the distances of each segment. If the spatial points are not being properly created, you could imagine that this would lead to undesirable calculations. 

Take a look at this link to make sure that the points are being created properly and add a browse tool to make a visual check of the map: https://help.alteryx.com/2020.2/CreatePoints.htm

[JDeJong]

See attached.