A physical boundary of a city can be determined by a geographical formation such as a river or a mountain. A figurative boundary is an imagined line that defines a city. Figurative boundaries are more complicated because there are several factors that can influence them.
While geographical formations are a common way of politically determining the parameters of a city because they can quite literally be seen, not all political boundaries are geographical. Some figurative boundaries are based on politics as well. Boundaries are set to define the jurisdiction of the local government. Other figurative boundaries are based on population. This is particularly true of metropolitan areas. Although a greater metropolitan area may include several cities or towns that surround a larger city, they are measured as a single area in order to determine the amount of people who contribute to the local workforce, economy and community.
Although imaginary boundaries cannot be physically seen or observed, they may be based on how some states parcel land. Currently, there is no nationally uniform way that this is done, though a federal system for land parceling has been proposed in order to more accurately define city boundaries in terms of jurisdiction and population.