The Netherlands has produced many of the world's most famous artists from Rembrandt and Vermeer in the 17th century to Van Gogh in the 19th and Mondrian in the 20th. Almost 20% of the total area of the Netherlands is water, and much of the land has been reclaimed from the North Sea. It has a significant role as a European transportation hub centered around Rotterdam Port and Amsterdam Schiphol Airport. Industrial activity is mainly in food processing, chemicals, the refining of petroleum, and electrical machinery. The services sector represents 70% of the economy. The agricultural sector is highly mechanized and employs no more than 4% of the labour force but it provides large surpluses for exports and the food processing industry. When it comes to the value of agricultural exports, the Dutch rank third worldwide. With no significant trade or investment barriers, the Netherlands remains a receptive market for exports and an important investment partner.