Which feature on a map would you use to measure the actual distance on the ground?

Using a bar scale on a map allows you to measure the actual distance on the ground accurately. A bar scale is a graphical representation of distance that is divided into segments, typically in miles or kilometers. By placing a ruler or straight edge along the bar scale and aligning it with the distance you want to measure on the map, you can easily determine how far that distance is in real life.

This feature is particularly useful because it takes into account the map's scale and can provide a reliable estimate of distance regardless of the specific area you're navigating through. It's crucial for planning routes, determining travel times, and assessing terrain.

The other options serve different purposes. Contour lines indicate elevation and terrain features rather than distance. The legend provides information about symbols and colors used on the map but does not assist in measuring distance directly. Grid squares may help in locating specific areas, but they do not offer a direct measurement of length or distance on the ground. Thus, the bar scale is the most appropriate tool for measuring actual distance.