One Surface Showing Multiple Spot Areas

Looking at the image below, at first, it may appear that you need multiple surfaces; one for each area (pond).  But in Civil 3D a single surface can represent multiple spot areas by using the OUTER and SHOW boundaries.

Two practical everyday uses:

  1. E&S Grading

  2. Spot Grading along a Corridor Model (endwalls, ponds, custom daylighting, etc…)

2009.10.19-Pond 1&2

To make this work it is as simple as placing an OUTER boundary around Pond 1 and a SHOW boundary around Pond 2.

In the example below we first use Featureline tools to grade in the two pond bottoms.


Next, we make an E&S surface – in this example called "ESC" – and add the breaklines (see the image for notes).

2009.10.19-ESC surface 

Finally, create two boundaries for the grading areas – in this case pond 1 & 2 – and add one as an OUTER boundary and the other as a SHOW boundary.

2009.10.19-BoundariesAfter the boundaries are added the surface should clean-up the spanning contours and you should be set to go.

2009.10.19-Final product

IMPORTANT NOTE: from this point you can add as many pocket areas as you would like.  Just grade in the area and add another SHOW boundary around your grading.





  1. Kevin Clark, P.E. says:

    Thanks. That will trick will save tons of time and reduce the amount of surfaces in a drawing.

  2. John Mayo, PE says:

    Mark, You may also note that if the limit of grading in either case is a closed feature line, it can double as a breakline & a boundary. A bit of time can be saved creating a new boundary.

  3. Yeah, some folks at my company do it that way, others – like me – use the pline as a boundary approach. I find it a pain to keep-up with that outer FL if it is also representing a boundary. Every time you edit a daylight for a small area you have to mess with the boundary. Get the FL re-joined together, add it as a boundary, move it to the bottom, etc… Where as a Pline you just drag it in or out after you get your daylight FL segment placed. To each their own… 🙂

    Thanks for the suggestion though. Others can see and incorporate into their workflow and make their own determination of which works better for them. 🙂

  4. P.E., P.E., P.E., a real brain trust here… 😉

  5. John Mayo, PE says:

    The PE’s know where to find what they need. 😉

    I am wondering if you found an improvement in Civil 3D here as well Mark. When we use to do this in LDD we needed more boundaries. You had to have a pline around both grading areas & make it an outer boundary. You then had to offset this inside a bit & make the offset pline a hidden boundary. After that you could define the show boundaries. I used this older method a few times in C3D 07 & 08 & I am not sure if it required 4 boundaries. Perhaps the two would have worked. I wonder if someone who had the old version(s) could see if the process works with two boundaries…

  6. We did the exact same thing back in Land Desktop days. OUTER–> HIDE–> SHOW, to make pocket grading. I wonder as well if we only needed two in LDT?

  7. John Mayo, PE says:

    LDT 09 still requires 4 for this.