# Best free sites/apps for surveying land



## bank5 (May 7, 2008)

I have a plat of my property and I'm looking to convert it to gps waypoints. I then plan marking things off. It doesn't need to be accurate and I'll err on the side of caution.

How accurate is an iPhone 6 within wifi, no wife but cell, and only gps?

What are some of the best free tools (websites and apps) for surveying land -- converting plat into waypoints, topo maps, satellite maps, gps navigation, etc?


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## Cotharyus (Jun 21, 2012)

Someone else may be able to chime in with this, but I think you can export routes on Strava's website. If you can do that, you can upload it into Gmap4, which is a website that should produce a pretty fair map for you. You may be able to combine that with tax plot information from a local GIS source and extrapolate everything you need to know.


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## Jelf (Jun 26, 2010)

Thanks to Cotharyus for mentioning Gmap4. I am the developer of that browser app.

Start Gmap4: http://www.mappingsupport.com/p/gmap4.php

If you can see your property lines on the Google aerial then you can trace them with Gmap4. Do Menu ==> Draw and save.
Accept the default of "Linepoints" and hit continue.
Click your property corners to draw a line around your land.
Each symbol is draggable.
Rightclick any symbol for a context menu.

When you have drawn a line around your land, then rightclick any point and select "Gmap4 link - No description".

Email that link to yourself and then *open it on your phone*.
Do *Menu ==> My location*.
The map will center at your posiiton.
Make sure the basemap is on the Google aerial (since you can zoom in more).
Now walk to one of your property corners as shown on map. *The symbol that shows your location will follow you as you move.* If you touch that symbol it will show your coordinates.

And if you cannot see your property lines on the Google aerial, then check out my other site: http://www.propertylinemaps.com/
I georeference land surveys and property legal descriptions using first-of-its-kind software I developed.

BTW, starting with the iPhone 4s, Apple phones can see both the USA GPS satellites and the Russian GLONASS GPS satellites. More satellites = more data = better accuracy.

Joseph


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## bank5 (May 7, 2008)

Very cool app Jelf. This should be very helpful.

My property lines do show up on Google Maps, however, the map is off. It cuts off about 40 feet of my front yard. The lines look accurate, but I'm not sure if it cut off the front yard or pushed things back 40 feet. 

When I used Google Maps on my iPhone early today and another thing that I noticed was my location was jumping around quite a bit. My property has a thin corridor to another piece of land, and sometimes standing in the same spot would either put my in my land or my neighbors land. Maybe a GPS app showing my exact coordinates would be more accurate? Or I could ask around to see if anyone has a better handheld GPS device.


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## Jelf (Jun 26, 2010)

bank5 said:


> When I used Google Maps on my iPhone early today and another thing that I noticed was my location was jumping around quite a bit. ... Maybe a GPS app showing my exact coordinates would be more accurate? Or I could ask around to see if anyone has a better handheld GPS device.


Thanks for the kind words.

In good conditions the GPS accuracy of your iPhone 6 is about 15 feet. A good quality handheld GPS will be about the same. Bottomline: *What you have is as good as a consumer GPS gets for accuracy.*

There are 2 things you can do to try to improve accuracy a little bit.

1. Make sure your GPS is on and set it outside with a clear view of the sky for 20 minutes. The purpose is to make certain your phone has a current almanac for the Russian satellites.

2. Download the pdf file I made with GPS tips and read about the effect that time-of-day can have on accuracy.
http://www.propertylinemaps.com/p/pdf_tips_for_using_a_gps.pdf


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## Harold (Dec 23, 2003)

Jelf said:


> *What you have is as good as a consumer GPS gets for accuracy.*


This is debatable. Waypoint averaging can really do a solid job of pinning down a location with a consumer GPS. It's not the submeter accuracy you can get with survey grade hardware, but you can get awful close. Phones are heavily limited by the antenna size that they have. Unfortunately, the size of the GPS antenna on phones isn't one of the items on the spec list. Some are better than others. An external antenna can help with signal quality, and some handheld GPS receivers have this capability.

Using waypoint averaging well requires that the corners at least be well marked on the ground so you can set the GPS in the correct spot. Was a survey recently done with the flagging left behind?

I did this once to mark my own property. It worked pretty well. I then used those GPS points to georeference the plat so I could use it in a GIS. Once I georeferenced the plat I got to see how well things matched up with the satellite imagery. It was pretty good. There was some distortion in the satellite imagery (the house dimensions didn't line up exactly right), but it was awful close.


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## bank5 (May 7, 2008)

So, I'm still trying to figure out if the property lines on the Google map is shifted or if it's truncated my front yard.

The plat shows that the distance from my front yard to the first point in the back is 63 meters. I get the same distance if I punch in the coordinates from Gmap4 and then calculate the distance - Coordinate Distance Calculator

If I measure via gps coordinates to the edge of the road, it's 77 meters.

Is the distance in a plat a 3d measurement (travel distance by land) or is it a 2d measurement (lat & lon)?

It seems like the property lines are shifted, in which case, I can figure out an offset to get the actual numbers.


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## Harold (Dec 23, 2003)

The edge of the road is technically not your property line. You have to account for the right of way. My place was the same. The corner flags were set back several feet. Google earth is probably not exactly correct. I could explain why but it is a lengthy one.


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## Jelf (Jun 26, 2010)

bank5 said:


> So, I'm still trying to figure out if the property lines on the Google map is shifted or if it's truncated my front yard.


Do you mean faint gray lines you see when you display the Google street map?

If so, those are Google's attempt to put your county's parcel data on the map.
1. The parcel data in the county GIS is often stretched/warped to 'fit' better.
2. We have no idea what adjustments Google might have made to that data.

Your property lines are where they are on the ground.
*A representation of your property lines on a map does not move your lines on the ground.*


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## bank5 (May 7, 2008)

Jelf said:


> Do you mean faint gray lines you see when you display the Google street map?


Yes, I mean the faint lines. Since they are off, seems like I'm better off using my plat.

I can get the starting coordinates with in a couple of feet. From there, I can get the next coordinate using a calculator like this - Find Terminal Coordinates, Given a Bearing and a Distance | FCC.gov

But that's not the ideal calculator since I'll need to convert feet to km and bearings and it rounds to the nearest hundredth of a kilometer.

EDIT: I found this which will do the trick - GPS Visualizer: Great Circle Distance Maps, Airport Routes, & Degrees/Minutes/Seconds Calculator


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## Jelf (Jun 26, 2010)

Also, land surveys use quadrant bearings. To use any waypoint projection tool you might have to convert the quadrant bearings to decimal degrees.

But there likely is a bigger problem.

The bearings in the great majority of land surveys are not based on true north. They are also not based on magnetic north. Instead they are based on an assumed north the surveyors call "basis of bearing". Worse yet, the "basis of bearing" used for your land may or may not be stated on whatever map or survey you are looking at.


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## bank5 (May 7, 2008)

Jelf said:


> Also, land surveys use quadrant bearings. To use any waypoint projection tool you might have to convert the quadrant bearings to decimal degrees.
> 
> But there likely is a bigger problem.
> 
> The bearings in the great majority of land surveys are not based on true north. They are also not based on magnetic north. Instead they are based on an assumed north the surveyors call "basis of bearing". Worse yet, the "basis of bearing" used for your land may or may not be stated on whatever map or survey you are looking at.


Interesting. The survey says magnetic north on it. I guess I could also convert magnetic north to true north -- seems like it's off about 8.1 deg W - NGDC Geomagnetic Calculators | ngdc.noaa.gov

I have seen a few metal pipes in the ground. I'm guessing they're surveyor pipes, so that should help too once I get the coordinate estimates.


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## BonkedAgain (Aug 23, 2005)

On a couple projects around here I found that what the county was providing as the boundaries of the land we were working on were way off, like hundreds of feet in one case and completely wrong (parcel wasn't shaped right) in another. The end result for the first one is the trail we thought was on private property actually wasn't. In the second case the trail that we thought would only be on national forest actually crossed property owned by the local city (another government agency to have to deal with). Sometimes it works for you and other times it's against you.

As far as consumer GPS accuracy goes, there are a lot of variables that influence it. I find that for general use my phone is fine. If I am out in the open then the accuracy is usually within 15'. If I do track averaging as mentioned above then I can really nail it down. In places where there is heavy forest or steep canyons the accuracy gets really bad, however, so keep that in mind.

I'm usually working on big pieces of land, like thousands of acres, so as long as I stay away from the boundaries I'm good from the property ownership perspective. If you are talking small corridors or urban areas then I would only use your GPS as a hint at where your boundaries are. 

If you need really good accuracy you should hire a surveyor, otherwise you are essentially guessing.


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