File this post under "random things that are good to know about Revit". Although, it seems to come up more than you would think...
Have you every had a topographic model within Revit not display the secondary contour lines? Look closely at the two topographic images above. What is different? Notice that the model on the left is missing three sets of secondary contour lines (the dashed lines that represent 1'-0" of elevation change).
Why?
Keep reading to find out....
Sometimes a user will start their topographic model with 0'-0" absolute elevation being equal to the finished floor of their building. Well, if your site slopes away from the building your next set of contours will be elevation -10'-0". In theory, this works for many projects if you are ignoring true elevation, etc... But, guess what.
Revit topography will not show secondary contours below 0'-0" elevation (essentially, contours with negative values).
Notice in the image below... The value of the points of the topography on the right are all positive, on the left, half of them are negative...
Weird.... No?
