What common understanding regarding map legends is often overlooked?

The common understanding regarding map legends that is often overlooked is that they explain the meaning of symbols and markings. Map legends, or keys, are essential components of any map as they provide information about what different symbols represent. This includes features such as roads, rivers, parks, and boundaries, helping users accurately interpret the map's information.

Without a clear legend, readers might misinterpret symbols, leading to potential confusion or errors, especially in navigation or when analyzing geographical data. Understanding this function of a map legend is crucial for effectively using any map, whether digital or paper. The other options do not accurately represent the fundamental purpose of a legend: while distances may be represented on certain maps, the critical purpose of detailing the meaning of various symbols is often what is most vital for comprehension and is frequently underestimated by users.