Demystifying Object Layers

What are object layers?  Why do my Express Tools (or Layer II tools) not work the way I expect?  When I pick a proposed alignment to freeze, all of my alignments disappear, even the existing ones? Why doesn’t matchprop work anymore? Why is Civil 3D treating me so poorly?? (followed by either cursing and a slamming phone, or tears and a trip to the shrink)

These are common questions from the new Civil 3D user… and often a point of frustration.

Here is an AutoCAD analogy that might help. Click here for more

When you create a block, you may use a few different layers while drawing the detail. Then, you define it as a block and insert it on layer zero. Layer zero acts like a “Master Layer” switch- if layer zero gets off/frozen, the block disappears completely regardless of what state those internal component layers are in.

Civil 3D object layers work very much the same way.  The Object Layer typically doesn’t control anything except visibility.  Meaning: Is the layer on/off?  frozen/thawed? Do I see the object or not?  It is a great way to turn off all of one kind of object in one click- like turn of ALL_PIPES to get rid of every pipe in your entire drawing, etc.

There are two exceptions to this behavior that I have found.  One is by design, the other seems to be a glitch.


If I have an with the Object Layer “C-ROAD” then apply a style that has layers mapped into it- the alignment ignores the Object Layer color/linetype/etc.

However, if I have a style where everything is mapped to zero, the object layer properties carry through to the alignment.  Things like matchprop and color changes to layer color STICK to the alignment.

So, in the typical case, C-ROAD (my object layer) can have any color and linetype assigned…

But as long as I compose my style to find the right layers…

My alignment (with that style applied) will always look the way I want.

If I change my style to map everything to layer zero…

The object layer now controls what things look like.

I am not sure I would operate this way.  A major part of Civil 3D’s appeal to me is that I DON’T have to think about layers, that a properly set up style does that thinking for me.  But you need to know that it is possible.


I have had this problem for a few months and finally yesterday I confirmed that I was not losing my mind.  No matter what you do to your structure style, the color, linetype and other properties will be controlled by the object layer.

So for now, make sure you assign an object layer for your structures that makes sense.





  1. MAnderson says:

    I think this is somewhat true as well for Surfaces. If you want to show the elevation information of a surface (An example is a floodplain at 50% shaded), the Surface Object Layer needs to be 50% shaded and the style of the surface (with contours etc) made to show as a Black Named Plot Style.

  2. Dana Breig Probert, EIT says:

    apparently the structure issue is a block issue… if you use the modeled part, the layer glitch isn’t a problem. i’ll post an addendum today.

  3. Michael Martin says:

    I’ve just spent a few days observing this behaviour for Structures – Ugh. Great to find your record indicating I’m not insane.

    Did you ever post an addendum, or am I just constrained to use the modeled part?