Which of the following principles suggests that properties should conform to similar properties in the area?

The principle that suggests properties should conform to similar properties in the area is conformity. This concept posits that a property's value is enhanced when it is in harmony with the characteristics of its surroundings. Essentially, when properties in a neighborhood maintain similar styles, sizes, and uses, it not only preserves the overall aesthetic but also helps stabilize property values.

In a neighborhood where homes are predominantly single-family residences, for instance, introducing a commercial property could disrupt the perceived value and desirability of the area. Therefore, conformity supports the idea that uniformity among properties contributes positively to their market value and appeal, making this principle vital in real estate assessments and development planning.

The other options refer to different concepts in real estate: contribution relates to how a particular improvement affects a property's value, competition refers to the influence of other competing properties on value and market behavior, and anticipation deals with the expected future benefits derived from a property. Each of these concepts plays a role in real estate, but only conformity directly addresses the relationship between a property and its neighboring properties in terms of value and desirability.