Understanding Alignments

You can think of the basic road geometry discussed in the chapter introduction as a single-line form of the roads, as shown in Figure 5.1. The lines that you draw will typically represent the centerlines of the roads, and eventually, you will build the rest of each road around those centerlines.

Civil 3D alignments are designed specifically for the task of representing the initial single-line version of a linear design feature. They are also used to establish the backbone of a linear design such as a road, railroad, channel, pipe line, and many other examples. The lines, arcs, and spirals that make up an alignment have the ability to interact with one another. This enables you to edit part of the alignment and have the other parts fix themselves automatically. Also, more design objects can be built around alignments, such as profiles, cross-sections, and corridors, which will be discussed later in this book.