How do I map my property?

July 11, 2005 3:51 PM

I'd like to make a map of my five acres but I have no surveying skills. Any simple guide to, or ideas about, amateur surveying on the cheap?

I have, of course, grabbed every satellite image I could of our property, but most of our acres are forested enough that some features, like an entire barn, are cloaked to the satellite. The satellite images did give me the basic layout and property boundaries, but I'd like to make a simple but accurate diagram of our forest trails, a few groves, gardens &c. Any ideas how? (Answers involving buying a transit and taking surveying courses are probably impractical.)

posted by argybarg to home & garden (15 comments total)

Well, according to this, all you need to know to be a surveyor is that 'Piss runneth downhill, and Pay-Day is Saturday.'

Seriously, though, a GPS unit that can do mapping should be helpful. Hikers often use them to make trail maps. You could use waypoints to mark trees, ponds, etc., then upload the data to your computer. The accuracy (within a few feet at best) might not be enough for a high-quality map though.
posted by driveler at 4:12 PM on July 11, 2005

My dad used to teach a survey course at the local community college. Half the year 3 or 4 transits and all the other equipment just sat in storage. If someone would have asked to borrow or rent one, I'm sure he would have worked something out with them. I think this was the book he taught from.

driveler's idea of using a GPS sounds much simpler. I've never used it but the GPS visualizer might be helpful if you do it that way.
posted by 517 at 5:03 PM on July 11, 2005

& check out SketchUp for your modeling needs. Very cool app.
posted by five fresh fish at 5:04 PM on July 11, 2005

Handheld GPS makes it cheap and easy. Just walk around and record the positions of trails and stuff. Then go home and mark them on a map. Repeat a few times if you want some better accuracy.

I wouldn't bother plotting stuff directly on the satellite photo. Just make sure you map a few landmarks that show up on it, then rotate and scale either your photo or the map until they match up.

I think the main point of the fancy surveying equipment would be to get elevations. GPS isn't so accurate for that, last I checked.
posted by sfenders at 5:27 PM on July 11, 2005

You might also want to start with the plat map of your land which should give you the offical legal outlines in some sort of recognizable scale. King County information is here [mini view of Vashon here, pretty amazing pseudo-interactive Vashon here, contour map here (giant)] and it looks like it would cost only a few bucks delivered. These maps are good because they will outline roads and a few other things, and then you can fill in the inside parts yourself.

These maps are legal documents that are filed with the County. They show the survey data, legal descriptions, restrictions, easement provisions, dedications, covenants (if any), roadway rights-of-way, lots, tracts and any other information pertaining to the plat. These maps may be ordered by Plat Name.

posted by jessamyn at 6:41 PM on July 11, 2005

You've got the basics from the satellite map. (If you haven't already, get aerial maps instead - far more detailed. Also check out your local council, and related websites, as they tend to have surveyer maps and over-laid aerial photos online)

Now, with a compass and 360-degree protractor (or a compass with a built-in protractor) you can pick a few points on the property to triangulate from. Put the protractor on a flat surface, at a location you know from the satellite map, and align it so that 0 degrees exactly matches the compass needle. Now, look at every object you wish you locate precisely on the map, and slight along the protractor (without bumping it), and write down the angles.

Do this from two or more other locations (the more the better) that you know from the satellite map. Some places won't be visible from all locations, so you may need a few extra locations. You want at least three sighted angles per object you wish to place on the map (hence "triangulation"). now your surveying is done.

Go inside, and set up your map (or what you have so far from th satellite map) on a drawing board or table. mark the sighting locations, and use the protractor and a ruler to draw out the angles from each location that you wrote down. Where the three lines meet is the location of your object. (Generally, error in your recordings will mean that they won't meet perfectly, but you just locate the object in the centre the triangle the lines form. If the triangle is too big, take some more sightings from other locations).

This method produces a map where the layout is accurate, regardless of scale (ie you don't need to measure distance, assume you have a good initial fix on your surveying locations). It doesn't take into account elevation.

You may find it easier to rig up a simple surveying instrument by mounting sighting pins in the protractor, and affixing it to a board via a pivoting pin in the center, thus you align the board via the compass (which could also be attached to the board), and then spin the protractor until the pins sight the object, and then write down the reading.

Also, bear in mind that the satellite photo may have warp or distortion. This will throw off your triangulation. If so, unless you can un-warp the photo with your computer (difficult to do precisely without ahem, a map to reference), it might be easier to survey the entire thing by triangulation. To do this you will need to establish sighting locations that you can accurately draw on your map. Probably the easiest way to do this would be to use a long rope to establish three equally distant points (a perfect triangle), and survey from those. When it comes to drawing the map, you can create a perfect triangle using a compass (the drawing instrument, not the surveying instrument), and then the initial survey sites are the corners of the triangle.

Doing the entire map by survey means you'll likely have to create other sighting locations. Each sighting location needs to be triangulated with the utmost precision you can muster, as with each generation further from the primary three, the margin of error grows larger. ie, try to have new sighting locations triangulated from the original three locations, rather than from locations that were triangulated from locations that were triangulated from locations that were triangulated from the primary three.

Play around a bit. You soon get a feel for how much accuracy leads to how much margin of error, and then you can put as much or a little effort into the surveying accuracy as you feel you need.
posted by -harlequin- at 6:55 PM on July 11, 2005

Actually, you might want to forget the compass, as nearby metal can screw it up without you realising. An alternative to aligning the protractor to North at each location is to align it to point to a sighting location instead (write down which one for each location) and then when you draw the map, use the protractor and rule the sightlines accordingly.

Either that, or pick a landmark so far away on the horizon that it's effectively the same direction no-matter where on the property you are. You'll need to be able to see it from all sighting locations however.
posted by -harlequin- at 7:07 PM on July 11, 2005

If your land has significant tree cover, then GPS likely isn't going to work (the satellite signals are masked). Also, the planimetric accuracy of the GPS positions you get from a handheld GPS receivers are only at the metre level (which may or may not be sufficient for your purposes).

Other options:

1. Aerial images, preferably orthorectified (corrected for relief displacement). These are available from a number of sources, and will, not surprisingly, show more detail than satellite images (ground resolution of some cm instead of some m).
2. A total station (a transit/theodolite that measures distances) and reflecting prism. You should be able to rent these from a local survey supply store. Provided you have some basic geometry skills, then these are really quite easy to operate. The most difficult thing will be setting it up and levelling it.
3. A transit/theodolite along with a measuring tape (chain, in survey-parlance). If it worked for surveying Canada in the 1800's, it will work for you. If you don't have a sufficiently long tape, again a survey supply store should be able to rent you one.

My advice? If your property is relatively flat, then try aerial images.
posted by Elpoca at 7:10 PM on July 11, 2005

Actually, I'd upgrade " the satellite photo may have warp or distortion" to "will almost certainly be warped and be unsuitable to survey from", unless it has already been un-warped to match a survey map. I'd suggest starting with a perfect triangle, and building everything from that. A good size for the triangle would be roughly the same size as the property, but if sightlines are obscured by forest, just something fairly large. You might find it useful to make some brightly coloured poles to stick in the ground, so you can sight locations through trees or over ridges.
posted by -harlequin- at 7:17 PM on July 11, 2005

If you can find an orthorectified aerial photo, send it to me with your points and I'll plot the trails and other features for you.
posted by atchafalaya at 7:41 PM on July 11, 2005

If you have a university or trade school nearby that has a survey course, you may be able to hire a student that can "borrow" some equipment from the school and do your survey for beer money. GPS may not work well in the wooded areas you describe.
posted by Yorrick at 11:55 PM on July 11, 2005

Hook up a cheap digital camera to a kite, or model helicopter/airplane if you're more ambitious (and have more money to spend).
posted by Civil_Disobedient at 4:59 AM on July 12, 2005

Don't know if this will link properly, but here's some examples of what you can accomplish (from the second link above).
posted by Civil_Disobedient at 5:04 AM on July 12, 2005

The state of Maine did arial photos of most of the state with quite high resolution. Your state may have something similar.
posted by theora55 at 5:28 AM on July 12, 2005

What is that link supposed to go to, theora55? I live in Maine and would love to have some high-res photos--Google Maps still has crap-o-rama satellite shots.
posted by Civil_Disobedient at 6:19 PM on July 12, 2005