OnX/GoHunt maps error?

[rideold]

Be wary of comparing aerial photography to parcel mapping. They both have their inherent set of errors. Remember that all mapping is based on a coordinate system and projection which is based on a model of the earth's curvature. None are perfect. Most parcel mapping coming out of counties is based on the State Plane System which works just fine for the scale at which it is intended to be used. Aerial photography is "warped" to a coordinate system after the imagery is captured and there will always be places where that doesn't quite look right. Think about it as a sheet of square rubber being stretched over a round surface.

In the end, the fence line is far more "legal" than OnX from the property owner's perspective.....that is if we're talking about things looking shifted in relation to each other on your phone screen. If someone has fenced an area of public land off (knowingly or un-knowingly) as their own that is a different issue and getting the county assessor or surveyor involved is the best course of action. But, if you are just trying to make sense of what is on the ground compared to what is on your OnX screen take it all with a grain of salt. While GIS means "Geographic Information System" is also can meant "Get It Surveyed"

 

[Dwnw/theAltitudesickness]

I believe he is trying to say that that imagery and the platted lines have to be in the same horizontal datum/coordinate system. In of of those images it clearly looks to be some sort of shift in either the imagery or the property lines. Both sides seem to be off roughly the same amount.

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Thanks @kwackkillncrew. This is what I am trying to find the wording for. It is about 50 yards shifted. I know in some systems (handheld garmin gps) you can select which datum you want to use. I think these 2 sources are not on the same coordinate system.

 

[kwackkillncrew]

I am not to privy with the coordinate systems in the lower 48 but if they do have state plane zone coordinate systems i would be fairly surprised if that was a choice on a hand held garmin. Typically i believe that those hand helds do everything is wgs84 (lats and longs). There might be a choice of WGS84 Nad27 or WGS84 Nad83 and if i remember right there is a bit of difference between the North American Datum 27 and 83. If there is platted Right of Way going North/South adjacent to that area you could go stand on the road and check to see if the road in the imagery is also shifted east/west like the cut line you found.

 

[LongWayAround]

In a handheld gps such as a Garmin, you are able to choose whether you want to view your coordinates in degrees,minutes,seconds or decimal degrees. Maybe there's another option or two. But as kwack mentioned, WGS84 is the standard and the options are just how you want to view those coordinates. Also, state plane wouldn't make sense as an option because it differs from ground distance by a variable amount and a local scale factor must be applied to get ground distance.

I'm not really up to speed on horizontal datums but in my area, the shift in vertical datum from navd 29 to 88 is about three feet with 88 being higher. I would imagine a similar shift in horizontal. And for fun, I believe a new datum is coming out in the near future.

In the example here, you have a flat satellite image of a three dimensional surface. Then, someone drew a flat shapefile of the parcels. Then, they overlayed them. There is often visual error unless they intentionally went in and rectified them.

 

[yfarm]

For historical purposes about fence lines

Gunter’s Chain Still Measures Iowa - Bur Oak Land Trust

Ever since the dawn of agriculture, people have marked out parcels of land to claim the fruits of their hard-earned labor. Soon thereafter, successful governments … Gunter’s Chain Still Measures Iowa Read More »

buroaklandtrust.org

 

[yfarm]

And more
The message sent by the California Courts in the past 20 years can be summarized thus:

1. If you have Survey monuments then those will likely hold as good evidence of location.

2. If you have just a fence:

a. If nothing is known about why, who, or why the fence was put there then it likely isn't evidence of the boundary. Sometimes there is evidence that affirmatively rejects the fence, most commonly it is in a convenient location.

b. If there is evidence that the neighbors were mutually uncertain and mutually agreed the fence is the boundary then it is the boundary.

c. There is no presumption a fence is the boundary just because it exists; direct evidence supporting b. above is required.

3. Boundary location is a question of fact; all of the evidence (both record and physical) will be considered.

 

[jayhawk]

I can understand gps being a few yards off. Phone locations and OnX are pretty approximate. But 300-400yards seems like a pretty big discrepancy.

You’re doing the right thing by erring on the side of caution though.

 

[Mike 338]

I often use paper maps and compass. When I see something of interest, I'll get a On X coordinate and then go back and put that waypoint on mapping software and print a map. What I've determined is that On X is frequently hundreds of yards off from my maps. I suspected it's because On X uses a different map datum that the USGS. I reached out to On X and in fact, they don't use the same datum as the USGS quad maps and unlike most mapping software options out there, On X doesn't give the user the option of selecting between different datums. That's pretty hick. Even the crappiest GPS unit will allow the user to select between different map datums because if you use the wrong datum, you'll be off, sometimes by a lot.

Bottom line... if you only use your phone with On X and never use a paper map, you'll probably be fine. Just hope your phone doesn't act up. If you use both On X and paper maps, you may well get lost. On X is OK for general public land/private land information but it can be pretty crap for reliable navigation.

 

[joeeger52]

I won a lifetime elite membership with OnX several years ago and I run it religiously in the backcountry. I’ve very rarely found discrepancies with private/govt land boundaries. However, I have come upon a location where I’m confused. I’ve found an area, which I know is bordering private land, it has a long straight cleared lane approximately 1-2 miles long (like you would fence) over several ridges. The East I have assumed was private. The West side being public.

Here’s my issue. OnX shows the line 3-400 yards further East than what I’m seeing in the field. I checked GoHunt’s data, exactly the same as OnX. The USGS topo map I have isn’t detailed enough for that small of a difference. Right now, im being smart and staying West of the visual line. I should add that there isn’t any signage or paint along this line. But I’ve let several nice bulls go due to this issue. My question…Is OnX and Gohunt using the same information? Any advice on how to verify? Could the line actually be further to the East and maybe I’ve encountered a fire break type situation?

I have found OnX to not be very accurate. I don't know what they use for their info, but I own 50 acres, and it is deeded as 50 acres. OnX says its only 43 acres. I am not trying to bad mouth OnX, as I use it religiously, but it is only used as a reference.