An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Johnson JH, Salt J.Johnson JH, et al. Among authors: salt j.Tijdschr Econ Soc Geogr. 1980;71(5):277-84. doi: 10.1111/j.1467-9663.1980.tb00900.x.Tijdschr Econ Soc Geogr. 1980.PMID: 12338538