Why is the proportion of self-employed workers more in rural areas?

In the rural areas majority of those depending on farming own plots of land and cultivate independently, the share of self-employed is greater. Most of the people are of the opinion that having your own business is considered under the head of "Self-employed" category. But, in reality all the people who do not work under anyone else are considered to be self-employed be it a vendor or a famer.