What tool is primarily used to determine distances on a topographic map?

The bar scale is the primary tool used to determine distances on a topographic map, as it provides a visual representation of distance that corresponds directly to the map's scale. By measuring the distance between two points on the map and comparing it to the bar scale, individuals can easily convert this measurement into real-world distances. This method is straightforward, allowing users to quickly gauge how far apart locations are without the need for additional calculations or conversions.

While a compass, GPS unit, and ruler can assist in navigation and measurement, the bar scale is specifically designed for this purpose on maps. The compass is used primarily for orientation and navigation, the GPS unit provides location information using satellites, and a ruler could be used in combination with the map scale but is not as intuitive as directly using the bar scale. Overall, the bar scale's prominence in mapping directly relates to its user-friendly nature for distance determination.