Final answer:
The function of scale bars on a topographic map is to help users measure actual distances on the ground by providing a ratio of map distance to ground distance.
Step-by-step explanation:
The function of scale bars on a topographic map is to provide a means to measure real-world distances on the map. They help users understand the ratio of distance on the map to the actual distance on the ground, allowing for accurate determination of the distance between two points, such as two hills.
The scale bar is usually accompanied by both kilometer and mile measurements to suit different users' preferences.