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Old 03-26-2011, 08:41 AM   #1
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Make Topo Site Map


Working on a large retaining wall at my own place. Engineer says he would like to see a topo at 2' intervals.

I'm thinking I'll set a parallel line to the side and of the house with 2' marks on it.

Then I'll string a second line with 2' marks perpendicular to the house and said parallel string.

By moving the 2nd string across the yard at 2' intervals, plumbing down from each mark and shooting an elevation.


I'll use the elevation at the back corner of the house as a benchmark and just note the +/- measurements for each point on graph paper. Connect all of the points on the graph paper that have the same mark. I should get the map.

Any suggestions? Improvements?
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Old 03-26-2011, 10:20 AM   #2
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Make Topo Site Map


An auto-level or builder's transit, along with a rod, can be rented for a very reasonable price(around here anyway). I don't think you would get the desired effect by measuring at 2' intervals though. You are on the correct track though, with the perpendicular grid lines. I'm also not sure if a home-spun topo map would fly, especially if the plan has to go through a permit process. I might be wrong though, it's has happened(or so the wife tells me) Cheapest alternative I can think of is to buddy up with a Civil Engineering student. Not really sure that would fly either. Checking with your Engineer to find out his preferred solution would be your safest bet, especially if the wall will have any height at all.
Not much help I know, but there are liabilities involved, both for you and your Engineer.I surveyed for a number of years.
Hit the local library in the engineering reference books and you can get a better idea as to what is involved in making a contour map.
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Old 03-26-2011, 11:09 AM   #3
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Make Topo Site Map


If your DIY survey (topo) is wrong, it will cost you more in change orders and delays than it would to have it done by a professional in the first place.

Drawing contour lines is part art. There are several methods to interpolate between the various elevation marks, but it still comes to judgment and experience.
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Old 03-26-2011, 12:52 PM   #4
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Make Topo Site Map


2' contours is not the same as measuring at 2' intervals. If you need engineering approval on something you are working on, you are going to be far better-off having a surveyor give you the data. If it's only in your back yard, it can't be very big/costly.

If the engineer just wants to see general elevation sloping for drainage approval or something, you county may already have 2' contours available. Most counties get LIDAR topography with aerial flights nowadays. USGS or your state geological survey may also be able to provide this.
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Old 03-26-2011, 01:18 PM   #5
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Make Topo Site Map


“Engineer says he would like to see a topo at 2' intervals.”

What the engineer means is that the finished map should have contour lines drawn at 2ft intervals. The number of data points and the process of collecting the information is something else.

The string line process you describe is not suitable to the task.

If you want to do the map, the place to start is an accurate horizontal plan at a suitable scale. You may be able to save a lot of work if you have a lot survey to start from.

As pyper pointed out, the process is part art. But it is not rocket science. Look for your survey plat and post some photos. Then I can better suggest how to proceed.
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Old 03-26-2011, 02:15 PM   #6
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Make Topo Site Map


I don't know if you are in Pittsburgh or if you are addressed to Pittsburgh but I found this map for city Pitt.

http://images.library.pitt.edu/cgi-b...opo&page=index

Especially in well established area, you can often find very good government created topo maps.

Now, what I linked may not be recent enough for your area but many major metro area are updated to be correct if there are major changes.

there appear to be many more links that might be helpful in a simple Google search

I know even in my little area of the world there is a topo map that is usable in my somewhat rural area.
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Old 03-26-2011, 02:40 PM   #7
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Make Topo Site Map


Thanks for all of the input guys.

I was able to import the terrain from Google Earth into the Sketch Up file I am using for the project but it is not detailed enough.

I am going to try and get a copy of the survey from the Township on Monday.

The final wall will probably be about 8' tall and around 14' long

I will post some photos and maps on Monday
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Old 03-26-2011, 04:12 PM   #8
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The simplest way to get an accurate topo map is with a builders level or a transit. Course you have to know how to use one. An alternative is with a rotating laser, easy to use, you simply measure down from the beam using a tape measure. You can also use a fluid level. Your string technique could work, but it would likely be slow and subject to inaccuracy.
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Old 03-28-2011, 06:05 AM   #9
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OK, doing some reading this morning. Amazing what you can learn in a book.....

Anyway, it looks like 2' intervals does not refer to the number of data points taken to create the map but rather the "change in elevation represented by each contour line".

SO if I can get my hands on an much more detailed Engineer Scale 1:600 Topo of the lot, I can fill in the blanks. Probably have to do something like shoot points perpendicular to a known contour line and fill in.

Off to the Zoning office today to see if I can get a survey.
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