Propinquity is the physical closeness of another person. When propinquity to another person is increased the greater the likelihood of friendship or attraction. Research suggests propinquity is the reason why people are more likely to befriend their neighbor than another person - the sheer closeness of the person will make you more likely to be attracted to them (either for friendship or romantic reasons). There are two factors that cause an increase in attraction to a person that is physically closer to you. One is simply repeated exposure - the more exposure to a stimulus the greater the attraction levels are. Another reason is anticipated future interactions with the person. Because we are aware of future interactions with those people near us it motivates us to like them and make the interactions positive.