On older maps, what color signifies populated areas, main roads, and boundaries?

The color red on older maps is commonly used to indicate populated areas, main roads, and boundaries. This usage of red is particularly prevalent in topographic and political maps, where it serves to highlight important features, making them easily identifiable. Populated areas and significant thoroughfares are essential for navigation and understanding the layout of a region, so the color red helps to draw attention to these critical elements. Additionally, red often represents boundaries or borders, further solidifying its role in the visualization of a map's features. This association with populated and significant areas has been a long-standing convention in cartography, making red an intuitive choice for map readers.