When a new design is started in Punch!, in LiveView a flat grassy surface under a partly cloudy sky is displayed. That flat grass surface defines what is called the Zero Plane, which is significant only because it is the reference from which all elevations are measured. At a later point slopes and berms (called "topographies" by Punch!) will move the grass away from the Zero Plane, which always stays right where it is, and so the zero plane will then be only an invisible, abstract surface, very much like the mile high plane (elevation of exactly one mile above sea level) which cuts through Coors Stadium in Denver, Colorado, and is marked only by a purple row of seats.
Before AS4000, I advocated elevating Punch! objects so that the Zero Plane always coincided with the top of the lowest floor in the structure (usually the basement floor). That way, the elevation measurement has real meaning for the user rather than just being some abstract number. Instead of having an "elevation of 24 inches", the main floor is now 120" above the basement floor. Doing this has another side effect. Punch! provides a set of measurements called Ceiling Heights for setting defaults in vertical measurement, including the default Working Elevation for each floor. However, if the basement floor is located below the Zero Plane, it is impossible to set a Working Elevation for it, as they are not allowed to be negative. Therefore, arranging the Zero Plane to coincide with the basement floor fixes that problem as well.
The only problem with doing this is that the terrain surface is already on the Zero Plane, making it natural to want to leave it there and move everything around it. However, the fix for this is as stated above - the grass can moved up and down from the Zero Plane with berms, so why not draw a berm over the whole Punch! lot, setting its height to the depth of the basement? It works just fine, because additional berms simply add or subtract from the new surface, just as they would if it was still the zero plane. And so, HighRise draws such a berm for the user at the height input for Basement Depth, and everything is properly anchored.
Alas, it worked fine until AS4000 was released. AS4000 introduced the Topography Designer, a very nice tool but for one thing - it removes berms (and slopes) as useful tools in Punch!, replacing them with the Designer's tools. Berms are no longer berms; they have been converted into contours, which do not add to each other, but rather are measured absolutely. Also, the terrain effects have been removed from the domain of Punch! itself into the Designer, making them unchangeable by Punch! PowerTools (except for the Designer itself, of course).
So, for Punch! versions at the 8.0 level and above, HighRise cannot do the berm for the user. They have to do it themselves in the Topography Designer, raising all the contours they may have produced by the additional depth of the basement. See this page for more detail.
As a sidelight concerning the Topographical Designer, nowhere in the documentation does the Designer mention the Zero Plane. That lead me and other users to believe that we could use "real" sea level elevations in the Designer, rather than artificial ones designed around the arbitrary zero plane. This turns out to be possible, but not useful. If that was done the sea-level elevation would also have to be added to all the elevations used in Punch! (like to every wall, object and so on), and it would make the elevation slider very un-useful except for ocean-front beach houses. The best way to work elevations is the old way - use the basement floor as the Zero Plane, compute the sea level elevation of that, if need be, and subtract it from all the contours on the USGS topo map used to set the lot's contours in the Designer. Then the basement depth will automatically be correct in LiveView.
In those cases where it is absolutely necessary to keep the Zero Plan where it is by default, or even somewhere else, HighRise has a way to handle that as well. Suppose you want the Zero Plan left alone, but bury a basement 48" below the terrain level. This can be done through a setting called the "bias", which allows the Zero Plan to move off of the basement floor.
More information about both can be read old and newterrain models in the Ten Commandments series of articles.
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