A map is an abstract representation of a physical area. Contrary to many people's assumptions, maps are not objective. What a map shows reflects the knowledge, biases and priorities of the person who made it. Physical maps show the terrain and characteristics of a location, while political maps reveal the human activities and national sovereignty of a particular place.
The man-made boundaries that are taken most seriously by human beings are those between countries. Although these boundaries are fictional from the point of view of the land, they become real in the minds of humans when they are made real on maps. Political maps of land areas are divided by national borders; these maps usually portray each country in a different color to emphasize their separateness. When two countries disagree about the exact location of a border between their territories, this situation can lead to tension and even violence.
Man-made boundaries that appear on maps of urban areas tend to reflect structures and developments that also exist in the real world. Unlike a boundary between two countries, which may be evident on a map but invisible on the ground, the streets, buildings and developments of an urban area are very tangible. A map that shows the layout of a city is designed for practical use, rather than for ideological purposes. The boundaries between informal neighborhoods will be invisible on the map, but the locations of streets, sometimes individual businesses, and buildings will be clearly depicted.
Man-made boundaries have frequently followed the contours of natural features. Prior to the development of satellite mapping and other technologies, people would often base their boundaries on rivers, mountain ranges or the edges of continents. This practice transforms a naturally occurring feature into a political reality. An example is the Rio Grande, a river that forms the boundary between the United States and Mexico. Political boundaries can also influence natural landscapes, for example along the politically determined parts of the border between the United States and Canada, where there is a strip that has been cleared of trees by humans.
A printed map gives the impression that man-made boundaries and political borders are immutable and unchanging, but this is an illusion. Examining a map of Europe from 1700 next to one from 2011 makes it clear that man-made boundaries change over time. These changes are usually the result of revolution, war or political upheaval that leads to one political entity taking over territory that previously belonged to another political entity. Following these disturbances, maps are redrawn and the new situation is eventually viewed as permanent, until the next disruption.