Which of the following best describes an isoline?

An isoline is defined as a line that connects points of equal value across a geographic area. This might refer to various datasets, including temperature, precipitation, elevation, or any other quantifiable attribute that can be represented spatially. By joining these equal-value points, isolines allow for the visualization of gradients and patterns within the data set, facilitating a better understanding of spatial relationships and trends.

For instance, in a topographic map, contour lines, which are a specific type of isoline, connect points of equal elevation and help convey information about the terrain's shape. Similarly, isotherms connect points of equal temperature, making it easier to identify temperature gradients in climate studies. This utility in representing continuous data is what sets isolines apart from other types of lines, such as those that might represent boundaries or specific species distributions, as indicated in the other options provided.