Author Topic: Discrepancies between gpx files and paper maps  (Read 2156 times)

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Offline alasdair

Discrepancies between gpx files and paper maps
« on: March 05, 2012, 04:30:14 am »
I'm planning a westbound TransAm ride and notice that the ACA gpx routes don't always match the route as shown on the paper map. A simple example is in Yorktown, Va (section 12, map 150) where the right turn from Main Street into a road leading to Water Street is at Compte de Grasse Street on the paper map and a block further on, at Read Street, in the gpx file. In this particular case, both options may be practical and it may not matter much which way you go. But other differences are more significant. For example, in Kentucky (section 10, map 125), the paper route between Harrodsburg and Bardstown passes several miles to the north of Springfield on SR438 but the gpx route (J0AC40) goes through Springfield. Which routing is preferable and why is there an inconsistency? I thought the ACA always revised the gpx files whenever the paper maps change. It doesn't look as though they do. I was hoping to use my GPS receiver as a backup to the paper maps to keep me from missing the way, but if the two go in different directions I may as well leave the GPS behind. Any information or advice, please?

Offline Fred Hiltz

Re: Discrepancies between gpx files and paper maps
« Reply #1 on: March 05, 2012, 06:16:59 am »
As one of ACA's legion of volunteers, I have produced many of the GPS routes. I can tell you a bit about the process and how differences arise. In a nutshell, the authoritative data are on the maps as amended, first by the addenda on the ACA web site and then by the Temporary ACA Route Road Closures forum group and the Twitter feed.

Upon reprinting a map or making a significant routing change, Jennifer sends the paper map out. We return the GPS revisions, which she submits to the web site. Occasionally, she changes the GPS data herself. The time that this takes is usually why differences arise. Look in the "About" file that accompanies the GPX files for the version number of the map that we used to make the GPX files. You may need to revise a few waypoints yourself from the addenda.

Simple human error happens, too. I have spotted a few problems, mostly on new routes, when making the GPS data. They get into the addenda quickly. Jennifer reviews my submissions for mistakes as well. Together, we do pretty well, but some updates might still fall into the cracks.

Later today, I will look at the differences you found and write back.

Fred

Offline mdxix

Re: Discrepancies between gpx files and paper maps
« Reply #2 on: March 05, 2012, 11:03:28 am »
All this blood, sweat, and tears to generate the GPX routes is labor of love!

Thank you Fred and your crew of volunteers. Hats off.

Offline Fred Hiltz

Re: Discrepancies between gpx files and paper maps
« Reply #3 on: March 05, 2012, 11:29:39 am »
Later today, I will look at the differences you found and write back.
These changes are in the "through the cracks" category. Carla just sent me the new map panel.

Alasdair, I can send a stopgap update file by email. Is the address in your forum profile OK for that? Or you can move the handful of waypoints yourself if you prefer.

When Jennifer returns to the office, we will look into rechecking all the older routes for missing updates.

This is a good reminder that the world changes faster than we can follow it, and no map--paper or electronic--is perfect. Your feedback via the map correction form on the web site is really important.

Also, you are probably aware than map makers scatter tiny errors to aid in prosecuting copyright violations. The case in point is not one of those, however.

Fred

Offline alasdair

Re: Discrepancies between gpx files and paper maps
« Reply #4 on: March 06, 2012, 11:32:12 pm »
Thanks for your help, Fred. We have exchanged emails about this and about an apparent error I spotted on the Yorktown map (paper and GPS routes) that I subsequently reported to the ACA. This is the first map panel I have looked at, at the start of my proposed ride, and I was naturally concerned at finding two issues so quickly. Let's hope there will be very few others. I appreciate the work involved, much of it voluntary, in trying to keep the maps and the GPS routes error-free and up to date.

Offline JMilyko

Re: Discrepancies between gpx files and paper maps
« Reply #5 on: March 07, 2012, 11:36:35 am »
All this blood, sweat, and tears to generate the GPX routes is labor of love!

Thank you Fred and your crew of volunteers. Hats off.

At this time, Fred IS the crew of volunteers for Routes & Mapping! We greatly appreciate him and all he does for us. And from me especially, his assistance with the GPS waypoint program has been invaluable!

.Jennifer.
« Last Edit: March 07, 2012, 11:38:46 am by JMilyko »
*_*_*_*_*_*_*_*_*_*_*

Jennifer H. Milyko
Adventure Cycling Association
Inspiring and empowering people to travel by bicycle.
800/755-2453, 406/721-1776 x205
www.adventurecycling.org

Follow Routes & Mapping on Twitter: @acaroutes

Offline JMilyko

Re: Discrepancies between gpx files and paper maps
« Reply #6 on: March 07, 2012, 11:57:12 am »
Upon reprinting a map or making a significant routing change, Jennifer sends the paper map out. We return the GPS revisions, which she submits to the web site. Occasionally, she changes the GPS data herself. The time that this takes is usually why differences arise. Look in the "About" file that accompanies the GPX files for the version number of the map that we used to make the GPX files. You may need to revise a few waypoints yourself from the addenda.

Simple human error happens, too. I have spotted a few problems, mostly on new routes, when making the GPS data. They get into the addenda quickly. Jennifer reviews my submissions for mistakes as well. Together, we do pretty well, but some updates might still fall into the cracks.

I've looked into this specific set of issues and it appears it goes all the way back to the 2008 reprinting and waypoint update. At that time, we had an intern working for us doing much of the gps waypoint updating. Also, the process was probably still a little bit fuzzy. It's gotten more consistent over the years but this situation has made me think I better add an additional review of the routing to my process. Errors can creep in from any human source.

In general, I would say when there is a discrepancy between the gps waypoint routing and what the paper map says, go with what's on the paper map. It could very well be that the route change did not make it into the gps waypoints.

I hope this helps. If you have further questions or concerns, please feel free to post them here, through the map correction form online (http://www.adventurecycling.org/routes/correctionform.cfm) or in an email to me directly.

Have a great trip!

.Jennifer.
*_*_*_*_*_*_*_*_*_*_*

Jennifer H. Milyko
Adventure Cycling Association
Inspiring and empowering people to travel by bicycle.
800/755-2453, 406/721-1776 x205
www.adventurecycling.org

Follow Routes & Mapping on Twitter: @acaroutes