A parallel of latitude is an imaginary line that circles the Earth, running parallel to the equator and measuring distance north or south in degrees. The 40th parallel refers to both 40 degrees North and 40 degrees South latitude. Since the 40th Parallel South lies almost entirely over the ocean, crossing only the southern tip of South America and a small part of New Zealand, this article focuses on the 40th Parallel North, which traverses major landmasses and is significant to human geography.
Tracing the Path Across Continents
The 40th Parallel North crosses the Atlantic Ocean, passing north of the Azores before making landfall in Europe. It traverses the Iberian Peninsula (Portugal and Spain), the Mediterranean Sea, Sardinia, the Italian mainland, the Strait of Otranto, Albania, the Aegean Sea, and Turkey, passing north of Ankara.
From Turkey, the parallel sweeps eastward across the Caspian Sea and Central Asia, crossing the following landlocked nations:
- Turkmenistan
- Uzbekistan
- Tajikistan
- Kyrgyzstan
It then enters China, traversing Xinjiang, Inner Mongolia, and Shanxi. After crossing the Yellow Sea and briefly touching the Korean Peninsula, the line continues across the Sea of Japan to Honshū, Japan.
The parallel crosses the Pacific Ocean before reaching North America, entering the United States near the California/Nevada border. It runs through the continental U.S., crossing states like Utah, Colorado, Indiana, and Ohio. It then cuts across Pennsylvania and New Jersey before exiting the continent.
Key Cities and Landmarks Intersected
The 40th Parallel North passes close to several major urban areas. In Europe, the line passes south of Lisbon and directly through Madrid, Spain. Further east, it touches the southern Italian regions of Campania and Calabria before crossing into the Balkans. In Asia, the parallel passes just north of Beijing and crosses the city of Tianjin, China.
In the United States, the parallel is marked by several features. In Colorado, Baseline Road in Boulder traces the exact path of the 40th parallel. In the Midwest, the line runs through the main campus of The Ohio State University in Columbus, cutting across the Oval greenspace. Further east, the parallel passes through Philadelphia, Pennsylvania, and the southern suburbs of Pittsburgh, Pennsylvania, and the northern suburbs of Indianapolis, Indiana.
Historical and Geographical Significance
The 40th parallel marks a transitional zone in global climate patterns. It separates subtropical influences to the south from temperate continental climates to the north. This separation influences agricultural practices and weather systems in the regions it passes through.
Historically, the parallel has defined political borders, particularly in the American West. It forms the straight-line boundary separating Kansas and Nebraska, established by the Kansas-Nebraska Act of 1854. Earlier, the line formed the original northern boundary of the British Colony of Maryland, leading to colonial land disputes.
The line also served as the route for the Geological Survey of the Fortieth Parallel, a major 19th-century scientific expedition led by Clarence King. This survey mapped the geology and resources across the Rocky Mountains and Great Basin. The data provided was foundational for the development of the American West.