[CastleBravo]

Long time lurker, first time poster. 

I don't think I have seen a post on this topic specifically, but was curious to see what thoughts were on this. 

It seems to me that if the earth is flat, and a disk, with the north pole in the center, that road that runs "straight" east-west (has the same latitude on each end), then there should be a detectable curve on the road.  Since the north pole is at the center of the disk, the further north you go, the more pronounced the curvature should be.  Seems like this would be a great way for someone to confirm or disprove the FE map. 

Here are my assumptions:

Earth Radius: 12,500 miles
Radius at a given latitude: (-12,500 * (latitude - 90))

Miles per degree of latitude: 69.4 (12,500 / 180)
Miles per minute of latitude: 1.157 (12,500 / (180 * 60))
Feet per second of latitude: 101.9 (12,500 * 5280 / (180 * 60 * 60))

So I took to Google Maps and started looking for some East-West roads with some long straight sections.  I found this 14.2 mile stretch in North Dakota:

https://goo.gl/maps/SM817Cs9mF22

Checking the center of the westbound lane at both ends resulted in latitudes of 48º 20' 32.75" N on the west end, and 48º 20' 32.41" on the East end.  A small, but significant difference.  When worked out using the seconds per minute above, the western end is 34.6 feet further north than the eastern end. 


On a flat earth, the radius at latitude 48º 20' 32.53" (between the two endpoints) is 2892.9 miles.  Using the Pythagorean theorem, I calculated how much the earth should curve to the right (if looking west):

D = Distance (miles)

Curve (feet) = 5280 * ( SQRT(2892.9² + D²) - 2892.9)

Distance 1 mile => Curve Offset = 0.9 feet
Distance 2 miles => Curve Offset = 3.7 feet
Distance 3 miles => Curve Offset = 8.2 feet
Distance 4 miles => Curve Offset = 14.6 feet
Distance 5 miles => Curve Offset = 22.8 feet

If you could somehow see the entire 14.2 miles of the stretch, the western end of the road should be 184 feet to the right of due west.  Was thinking that you could use GPS to validate that the latitude of the road doesn't change over its length.  (I don't know that I have seen anyone on here dispute that GPS works, just arguments about how it works)

Anyway, it is just a thought exercise right now, unfortunately I don't have and good hills with straight, east-west roads coming down from them around here, or a tower or something tall in line with an East-West road to use.  I was wondering if anyone else has done this.  Seems like a pretty definitive way to prove/disprove the FE map.

[HorstFue]

Don't invest too much in prove/disprove flat earth map.
Even FE admit, that there's no (detailed) flat earth map available.
You might have a look at this thread
"Why is there no flat earth map"
https://forum.tfes.org/index.php?topic=9014.0

[6or1/2Dozen]

GPS is commonly disputed as inaccurate around here, recently as last week even:

We can all agree, flat-earther and round-earther alike, that GPS, GLONASS, Galileo and similar systems work pretty well.

I don't agree with that. There are numerous complaints online that GPS gives inaccurate distances. Look at this link: https://pmags.com/gps-mileage-discrepancies

Multiple examples are given, including the following quote:

And in the racing world, professionally surveyed half-marathon routes of 13.1 miles are called too short by people wearing GPS enabled devices.  Some people less politely and less friendly, but still firmly, write the race directors and complain that the race course is 13.9 miles or even 14.2 miles. Some racers even are LESS polite. :O  Why? Because their GPS enabled devices report higher mileage than what is on the race course.

USATF Certified tracks are measured with wheeled devices, and this distance differs when compared to GPS.

This author claims that GPS devices are inaccurate for finding distance, and that this inaccuracy grows with greater distance traveled (which is curious under the Round Earth model since GPS is just finding your coordinate and computing the distance to another coordinate).

Another quote from that link:

Your GPS-enabled watch, a GPS unit such as one bought at outdoor stores or an increasingly frequently used mobile devices are all Recreational Grade GPS units. They are good for knowing, more or less,  where you are in a general location.  You will not get pinpoint accuracy for location or distance.  The effects of this inaccuracy is more noticeable the longer or more varied a jaunt.

See the bolded. If the Round Earth model is true, this is confusing, since GPS devices are just based on finding your coordinate and mapping how far away coordinate B should be. It should not matter how far away you map coordinate B. It should not increase in error the further away you map. The coordinates and the distance between them on a Round Earth should be known.

A comment at the bottom of that article showing that this is illogical:

It surprises me how much inaccuracy there seems to be. If my GPS knows my position within fifteen feet, there shouldn’t be a half mile discrepancy over fifteen miles.

The author of the article further asserts that "professional GPS equipment" is necessary, but does not suggest that he has ever used it, or show information that it is any more accurate for distances. Such equipment may be more accurate for showing current coordinate with higher resolution, beyond the accuracy of consumer GPS (which measures in 3 to 7 meters, not on the range of miles), but it does not follow that such professional devices are more accurate for "measuring distances". The distance between coordinate points on a Round Earth should be known in all systems.

[CastleBravo]

Don't invest too much in prove/disprove flat earth map.
Even FE admit, that there's no (detailed) flat earth map available.
You might have a look at this thread
"Why is there no flat earth map"
https://forum.tfes.org/index.php?topic=9014.0

I know that there are many FE maps, but I used that one because it is the most common one, it is in their wiki, and the UN uses it on their flag. 

And it is not really a waste of time - I enjoy math and science, and I find it interesting to test the flat earth theories and try to find new ways to look at FE maps and models.  I just found it interesting that a flat earth should still have curvature, and should be pretty easily detected. It seems like it would be a pretty easy way to disprove this particular map (or add evidence for it).

[CastleBravo]

GPS is commonly disputed as inaccurate around here, recently as last week even:

We can all agree, flat-earther and round-earther alike, that GPS, GLONASS, Galileo and similar systems work pretty well.

I don't agree with that. There are numerous complaints online that GPS gives inaccurate distances. Look at this link: https://pmags.com/gps-mileage-discrepancies

Multiple examples are given, including the following quote:

And in the racing world, professionally surveyed half-marathon routes of 13.1 miles are called too short by people wearing GPS enabled devices.  Some people less politely and less friendly, but still firmly, write the race directors and complain that the race course is 13.9 miles or even 14.2 miles. Some racers even are LESS polite. :O  Why? Because their GPS enabled devices report higher mileage than what is on the race course.

USATF Certified tracks are measured with wheeled devices, and this distance differs when compared to GPS.

This author claims that GPS devices are inaccurate for finding distance, and that this inaccuracy grows with greater distance traveled (which is curious under the Round Earth model since GPS is just finding your coordinate and computing the distance to another coordinate).

Another quote from that link:

Your GPS-enabled watch, a GPS unit such as one bought at outdoor stores or an increasingly frequently used mobile devices are all Recreational Grade GPS units. They are good for knowing, more or less,  where you are in a general location.  You will not get pinpoint accuracy for location or distance.  The effects of this inaccuracy is more noticeable the longer or more varied a jaunt.

See the bolded. If the Round Earth model is true, this is confusing, since GPS devices are just based on finding your coordinate and mapping how far away coordinate B should be. It should not matter how far away you map coordinate B. It should not increase in error the further away you map. The coordinates and the distance between them on a Round Earth should be known.

A comment at the bottom of that article showing that this is illogical:

It surprises me how much inaccuracy there seems to be. If my GPS knows my position within fifteen feet, there shouldn’t be a half mile discrepancy over fifteen miles.

The author of the article further asserts that "professional GPS equipment" is necessary, but does not suggest that he has ever used it, or show information that it is any more accurate for distances. Such equipment may be more accurate for showing current coordinate with higher resolution, beyond the accuracy of consumer GPS (which measures in 3 to 7 meters, not on the range of miles), but it does not follow that such professional devices are more accurate for "measuring distances". The distance between coordinate points on a Round Earth should be known in all systems.

Wanted to reply to this as well, had to read through the links in the above quote.  Yes, I agree that GPS is inaccurate for determining distances when it samples your position every so often and calculates the distance.  I have a hand-held GPS unit and when I stop for lunch when I am hiking, I can add 0.1-0.2 miles to my total distance because the unit is continuously recording my location (all within a 25ft radius or so).  None of the recorded points are exactly in the same spot, so it thinks that I am walking 10ft to the left, then 20 seconds later, walking 10ft forward, etc...  But, they are always within about 25ft of where I actually am.

However, I was suggesting using the GPS to determine the latitude of each end of the straight stretch of road - basically taking two points, each of which should be accurate within 25ft or so.  If the latitude is the same on each end of the road, then the road should be East-West.