Each culture, and even within cultures in terms of rural and urban living, has different levels of physical closeness appropriate to different types of relationship, and individuals learn these distances from the society in which they grew up.
In today's multicultural society, it is important to consider the range of non-verbal codes as expressed in different ethnic groups. When someone violates an 'appropriate' distance, people may feel uncomfortable or defensive. Their actions may well be open to misinterpretation.
In Western society, four distances have been defined according to the relationship between the people involved, the study of personal space is termed proxemics. What is it in your culture?