Discover how civil engineers use different types of units to represent distance and direction in site plans. This article takes an in-depth look at the use of decimal units and the surveyor's system for precision and clarity in civil engineering drawings.
Key Insights
- Civil engineers typically use decimal units in their site plans, where one decimal unit represents a foot. The precision is usually set to hundredths of a foot to ensure accuracy.
- The surveyor's system is often employed for measuring angles. In this system, direction is represented as north or south followed by degrees, minutes, and seconds towards east or west. This system is commonly used to denote the path of a property line.
- The path of surveying can be done in both clockwise and counterclockwise direction, and the angle direction will differ based on which direction is being followed. However, the final point must coincide with the point of beginning, if not, it indicates a problem in the measurement or drawing.
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Civil engineers who work on site plans, what we also call metes and bounds drawings, use different kinds of units. When you look at the interface box, you'll see that the standard units that we have been using are architectural, and our precision has been set to 1/256. What civil engineers do is they choose decimal units.
For us, an architectural unit is one inch. For them, a decimal unit represents a foot. So they would have decimal units.
And then we have the precision. Normally, the civil engineers present their units to two levels of accuracy, so where the units are decimal, one decimal unit would represent a foot. And then you can see with the precision going to hundredths, that means hundredths of a foot.
That's how they are interpreting their units. Then we have the angle type, and this is what we're going to focus on the most right now. Their angle type is surveying units, and their precision is normally just like ours, north, so many degrees, minutes, and seconds.
And the example they're using here is east. So again, we have set our units on a civil engineering drawing to be decimal. So the type of unit is decimal, where again, one decimal unit represents a foot.
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The precision is to hundredths of a unit. And again, they're interpreting this to be hundredths of a foot. The unit types they use are surveying units, and I'm going to go OK.
Now, I have a site right here that's relatively simple, and the site is a rectangle, just so we can begin understanding what's happening. When surveyors begin doing their work, they start off with something called a point of beginning, or POB. And what they do is they work their way around the property.
So these arrows represent the order in which the surveyor, in this particular example, would be measuring the length and direction of the property line. They would start at the point of beginning. They would go up, measure to here, go this way, measure to there, go down here, measure to there, and then come back and close it at their point of beginning.
Now, when I look at the line segment that is going this way, this segment is going north so many degrees east or west. Because typically, when engineers are working, they're saying north so many degrees east, north so many degrees west, or south so many degrees east, or south so many degrees west. So in this example, we have right here, we're going from the point of beginning north 0 degrees east.
And that will get us to this point. To continue on, they would be going, in this example, north 90 degrees east, which would take us over here. From here, going down, they would be going south 0 degrees east or west.
And to continue on, they would go from here to the left, which would be south 90 degrees west. So this is a very simple example based on a rectangle that is perfectly north and south. You know as well as I do, though, that most properties don't go straight up and down, north and south, left and right, east and west.
Normally, they will be relative to different angles. Now I have taken this very same property and I've rotated it 30 degrees. So let's zoom in.
I have my point of beginning. And again, what we're doing in this example is we're going clockwise. We're going clockwise around the property.
If the surveyor starts at the point of beginning, and again, everything in this example is rotated 30 degrees, to go from my point of beginning to my point up here, I'm going to be going in the direction of north 60 degrees west. Because again, when you look at the compass, you can see that this line segment is in the top left quadrant, and it's going north 60 degrees west. If I pan over to here, this next segment is going north 30 degrees east.
So this segment right here is going north 30 degrees east. I'm continuing in the same direction. For this next segment, I'm going south 60 degrees east.
So again, this segment here is in the bottom right quadrant. So it's south 60 degrees east. I continue on.
This next segment is in the bottom left corner. So it's going to be going south 30 degrees west, and it's ending up at the point of beginning. Whenever we do metes and bounds drawings, we do not do a "C to close."
What we want to know is that if the property lines do not close, we need to find out what the problem was. So again, we would not draw three segments and then go "C to close." We would always want to have this last segment with its own appropriate distances and directions.
And if there is a gap down here in the bottom, we need to know about it. What I've just done is turn on some layers showing the opposite direction. Now, everything we've been showing so far, their path of travel has been in a clockwise direction.
I want to show you traveling counterclockwise instead. If I start at my point of beginning, you can see here by going in this direction that I'm going to be going north 30 degrees east. Now, let me just pan back a bit.
When I was coming the other way, this line segment was measured as south 30 degrees west. So I was going south 30 degrees west. Whereas when I'm going counterclockwise, it's north 30 degrees east.
I will continue on. This segment here is in the top left quadrant. So it would be north 60 degrees west.
This segment down here would be south 30 degrees west. And this last segment would be south 30 degrees east. So again, what I'm hoping you can see is that when I have a segment that's going clockwise, this segment would be north 30 degrees east, whereas the same segment being measured the opposite way would be south 30 degrees west.
