Corridor surface for an entire subdivision

[cneelyUFTR2]

I have a colleague who wants to expand a corridor surface to the entire subdivision. They want to add feature lines for the lots, swales, etc., and have all the proposed grading in that one surface. This seems wrong to me. I’m of the opinion that creating surfaces separately and combining them to form the FG surface is the best practice. It just seems taboo to me to do any edits to the corridor surface, that aren’t derived from corridor editing.

What are your thoughts and opinions?

[Kevin.Spear]

First, to be clear, a corridor is made up of baselines that you run an assembly along to generate surfaces, quantities, etc. Certainly, one corridor object could be ALL of the roads in a subdivision. You may be able to do the same for lots if it's rough grading. However, in my experience, any grading outside of the ROW are individual surfaces (lots, open space, detention basin, etc). These individual surfaces are then combined with the road corridor into a composite FG.

Typically, the reason to make a single corridor for an entire development has more to do with how you want to quantify that data. No wrong choices, but being aware of municipal reporting requirements may be affected downstream in your c3d model. 

[cneelyUFTR2]

Doing corridor surface editing outside of the corridor is my issue. Adding feature lines and such to extend the surface beyond the true corridor limits created by assemblies just doesn't seem like a wise idea. 

[Kevin.Spear]

Let me make sure I understand, he's adding surface data directly to the corridor surface? Yes, that can be bad. Especially when it comes to corridor surface boundaries. I would also stay away from muddying the corridor surface directly, or even a surface from grading objects. just make a separate surface and combine them in a composite surface. Less room for corruption when data is isolated.

[BrianHailey]

In my opinion, your corridor surface should be exactly that, the corridor surface. You base your lot grading off the elevations of the corridor so if you have the lot grading in the corridor surface, how do you determine what the new elevation for the lot is when the corridor changes? One thing I did do to my corridor surface was to create a featureline around the limits of the grade, assigned it the elevation of the existing ground, and added that to my corridor surface. I then created a separate surface for each "island" of lots within the corridor (and I did these in separate drawings so more than one designer could be working on it at a time). Once done, I then created my final surface in a new drawing, data referenced in the corridor surface and all the other surfaces, and then pasted them all into the final surface. 

[cneelyUFTR2]

Yes, adding data to extend beyond the surface created by the corridor. The corridor limit is the ROW and provides an FG to the ROW. And then adding feature lines to represent the pads, lot lines, swales, etc., beyond that. 

They provided samples from their previous firm that did just that. But just because it "worked" doesn't mean its a best practice, or even a right way to do it. I feel it's wrong. 

I appreciate the feedback, it will be helpful.

[BrianHailey]

I understand being burned by a limitation of the software at one point and then being leery to use it again later (ask just about anyone here about grading groups). With that being said, I have seen no issues with pasting surfaces that haven't been a result of either bad implementation or bad data. If they question you on this, point them to this thread and let them read it themselves. The people that have post here are some of the smartest people when it comes to using Civil 3D and the overwhelming consensus is that pasting surfaces is the way to go.