What is the main characteristic of township lines in a rectangular survey system?

In a rectangular survey system, township lines are primarily characterized by being parallel to the base line, which runs horizontally. This means that township lines are laid out in east-west orientations across the survey map and remain consistent in their proximity to one another, creating a grid-like structure. This uniformity allows for the straightforward division of land into townships, which are six miles square.

The parallel nature of township lines is essential for consistency in land surveying and zoning, ensuring that each township can be easily identified and referenced. This system facilitates property management and real estate transactions, as it eliminates confusion regarding boundaries.

The other options do not accurately describe township lines: they do not change over time, they are not curved, and they maintain a fixed distance that does not vary in length. Understanding the characteristics of township lines is fundamental in comprehending how land is organized and surveyed in the rectangular system.