For my past three articles, I have covered proposed grade contours. For some, this may seem like three too many articles on something so trivial as contours. But as I have pointed out time and time again, if there is one consistent trait of a less effective data builder it is an overreliance on contours. The worst examples I have seen of broken data was when the data builder simply made a surface out of the contours, shipped out the model and sent a bill to his client, for miles of heavy highway no less. Rather than ignore this problem, the goal of my past three articles was to try and show that contours should be only one part of the bigger puzzle - specifically the last part.

To continue my discussion of contours, I want to address the last type of project: subdivisions. Subdivisions are somewhat unique in our project types in that they can vary greatly in both detail and scope. A subdivision in Arkansas may have only a series of roadways and no detail for the lots once you move outside of the roadway daylight line. A subdivision in California on the other hand, will typically have not only exhausting detail for the roadways and intersections themselves, but also very detailed pad, side lot, rear lot and lot drainage grading information which all amount to more spot elevations than can be counted. If there ever was an Olympic event for data building, the project site is somewhere in California J.

As with the other project types, it is entirely possible that you could have no contours at all for your subdivision - everything is built off of the plan and profile with spots. This is very typical for subdivisions that have great detail provided for the roadway and lots, such as the above mentioned typical subdivisions from California. But even then for California, it is still the exception and not the rule to not have any contours. Much like sites, you can almost always count on having at least a few proposed grade contours running through your subdivision site. So we once again ask the question: how can a good data builder work proposed grade contours into his subdivision model?

If you have read my last three articles on contours, you already know what the answer is going to be but I will say it anyways: proposed grade contours should be the last resource used when building your subdivision model. Going by the universal data builder’s rule of using the greatest amount of detail first, for every subdivision I have ever seen this will be the road ways as defined by plan and profile. From a mathematical point of view, as long as the engineer provides all the necessary pieces, the combination of plan, profile, typical section and cross sections provides an accurate elevation for every square inch of the roadway. High point, low points, super transitions, intersections, you name it. They can all be recreated without a single other source of information. This same feat is impossible using contours of a realistic interval. If roadway design by plan and profile is new territory for you and generally you use contours to detail out your roadway then there is a huge opportunity for error in dozens of situations. If this is your case, its time to get some training on building them from your software developer. Regardless, with a proper plan and profile, you can confidently and more importantly, accurately recreate the roadways of your subdivision project. This for me is always step number one of building a subdivision.

Next, let’s address the lot grading. This is where things can start to vary greatly. You may have no lot grading at all. You may only have contours to detail the lots out. Or you may have literally hundreds of points defining not only the building pad, but all sides of the lot to boot. As will come as no surprise, if you have pad elevations or spot elevations, these will need to get in there first. Once again, they provide greater detail than the contours can. Obviously care is needed to ensure that the correct breaklines are provided since you are dealing with (typically) such a small area on each individual lot.

After the pads and spots are in place, and the roadways are done, it is now finally time to put those contours to good use. Site features such as parks, retention/detention basins, berms, ditches and so on can now be fully detailed out using the proposed grade contours. For any component of my project that was designed by anything but contours, the contours can make for a nice and quick double check to ensure that my calculations (especially for the roadways) were correct and the engineers typical sections match their actual design. Any contours that exist within the roadway or lots previously designed should be clipped out to ensure that they do not interfere with your previous, more detailed design work.

Ultimately, no matter whether you are working on a roadway, site or subdivision, contours are almost universal in any project. However, care must be taken when using them to ensure that they are used correctly, if at all. Since a good data builder always starts with the most detail, and ends with the least detail, proposed grade contours are at the bottom of the food chain. Still, their proper use can greatly increase the accuracy of your model when other, more accurate information from the engineer is not available. If contours have been your first step in data design, then its time to have a fresh new start on a brave world where contours come last instead of first. By doing so, you ensure that your models are more accurate, more complete and more likely to be free from error.