Higher than average percentages are employed in education (17.9% vs. 12.7%); health and welfare (12.6% vs. 10.7%); community and social services (6.4% vs. 4.7%); hotels and restaurants (6.1% vs. 4.7%); and public administration (8.2% vs. 4.7%). During the British Mandate, a law was passed requiring all buildings to be constructed of Jerusalem stone in order to preserve the unique historic and aesthetic character of the city. Complementing this building code, which is still in force, is the discouragement of heavy industry in Jerusalem; only about 2.2% of Jerusalem's land is zoned for "industry and infrastructure." By comparison, the percentage of land in Tel Aviv zoned for industry and infrastructure is twice as high, and in Haifa, seven times as high. Only 8.5% of the Jerusalem District work force is employed in the manufacturing sector, which is half the national average (15.8%).