If it's 2 acres and 450 feet one way that means it's about 200 feet the other, assuming it's rectangular. With a measurement every 20 feet that's 23x10 measurements, or 230 total. If you spend 10 minutes on each measurement that's 38+ hours, or about a week. So the challenge is doing it in a reasonably efficient manner so it doesn't take you forever. There are really two parts to this. One is laying out a 20x20 grid with reasonable accuracy. The other is taking height measurements with reasonable accuracy.
Here's how I would do it, assuming the ground is reasonably clear, flat and free of obstructions. You can get a laser that will shoot the 200 foot direction. I would mark two corners along the 450' dimension. I would walk that line with a
measuring wheel , and use a
spray paint marking wand to put a dab of paint every 20 feet. Then I would do the same thing along the other 450' edge.
(One thing you'll have to ask yourself is how important it is to make a true rectangle at this point. If you don't want to just eyeball it, and you don't have any landmarks, once you've got your first two corners down you'll want to use a 3-4-5 triangle to find a right angle to them, and then use the measuring wheel and the laser to measure out two perpendicular sides of the same length, and then the laser to connect them.)
You'll need two
laser target cards and two stakes, probably six feet or so. Use a ruler and a sharpie to turn one stake into a measuring stick. Put the target card on the other and pound it into one of your paint blobs. Put the laser on the matching blob on the other side of the lot and see if you can hit the target. Now walk from the laser to the target carrying the measuring stake, the other target, a notebook and pen, and measuring with the measuring wheel. (You'll need four hands!) Every 20 feet stop, get the target into the laser beam, and use the measuring stick to measure the height above ground. Record in the notebook. When you reach the other end move the stake to the next blob, move the laser to the next blob and repeat until finished.
A helper would be real handy, because otherwise you have to make a round trip for each pass to move both ends. With a helper you can do each pass in a single trip so you save half the walking. Even so it's about a mile of walking.
