For my third article on contours, I wanted to cover the second, and for most data builders, the most common project type: the simple site. I would argue that no matter where your beginnings as a data builder were, you cut your teeth on simple site projects. They are small. They are generally straightforward. And most of all, they are predictable and consistent when it comes to design techniques. However, in my opinion, because of their straightforward nature and small size, simple sites are begging for improper data building techniques. It is too easy and tempting to get lazy in your design and sloppy with the model because of the nature of the project. While we could spend multiple articles detailing out the many aspects of simple site design as a data builder, in this article I will only address how proposed grade contours from the engineer could and should be used.

First, as I mentioned in my previous article, we break all projects down into one of three types for both building and billing purposes: roadway, site and subdivision. Since this article will be dealing with sites (for roadways, see my previous article), lets start by defining a site as a project that does not contain significant portions of roadway defined by a profile. This loose definition certainly takes in project types ranging from mine reclamations to airport taxi pads and from huge landfills to the convenience store on the corner. However, by far the most common projects will revolve around a commercial site with the major components of a parking lot, building pad and any site grading (such as detention/retention basins). While the engineer will sometimes use a profile to define an entrance road on a commercial site, this is the exception and not the rule. Which is again why most start with simple sites to learn the basics of building data.

As you can imagine, on site type projects your bread and butter for grade information is proposed grade contours and proposed spot elevations. Obviously there will be cases where you only have one and not the other. It is actually pretty typical fare to only have spot elevations for a California commercial site. If you only have one source and not the other, the choice of which to start with should be pretty easy. But for every simple site project that we do with only a single source of grade information, we do another twenty that have multiple sources beyond just the proposed grade contours. In those cases, where do you begin?

While everyone who builds data has their own technique, allow me to make a strong recommendation: start with everything but the contours. I will say it as many times as is needed: they should be your last source of information for nearly every project you build. Instead of starting with contours on a site, get those spot elevations in there first. For a site project, they are your most accurate source of grade information because they associate a specific elevation with a specific location. Without a profile, this makes them the most specific grade information provided by the engineer in the plan set and they have to be correctly represented in your design. If the plans say that the top back of curb should be 1234.52 you had better believe that the contractor is going to want to go out in the field and have his GPS rover show him 1234.52 for that curb location. Obviously when you have very few, or even no spot elevations then you are limited in your choices and have to use contours as your primary source of grade information. But whenever they both exist, spot elevations should go in first every time. Even if I was building a commercial site that had only two spots and hundreds of contours, I would take the twenty seconds and get those two spots in there first.

But what do you do when you have both contours and spots provided, but they don't agree? I know you think I am going to say throw out the contours every time, but that is not always the best thing to do. With a project of this type where you typically only have these two sources of grade information and they conflict, you need to look at the bigger picture and see which source seems to be correct. If the contours are defining a nice smooth parking lot but you have two spot elevations that stick up in the middle of all that, my best guess would be that the spots were likely fat fingered or entered in error and should be thrown out. Or if you have a very consistent slope defined by spot elevations going down a run of curb but have a contour that crosses the curb and is a order of magnitude off from the established slope, I would throw that contour (at least at that location) out in a heartbeat. In other words, when conflicts arise on sites you have to address each one individually because either source could be in error.

Ultimately, even on a simple site project proposed grade contours still should not be your primary source of grade information. Don't get me wrong, they have their use even with simple sites. But due to their inherent inaccuracies, it is difficult to accurately recreate an engineers design based solely on them. This is especially true for a parking lot where you have to determine the elevations along curb lines which do not follow contours nicely. So in the end, when building models for site design, take all your other grade information first and then in the end, finally let the contours take part also.