The imaginary line of the Earth's surface that closely follows the 180° Meridian is—

The International Date Line (IDL) is an imaginary line on the Earth's surface that closely follows the 180 meridian [1]. While the Prime Meridian is designated as 0 longitude, the 180 meridian (also known as the antimeridian) is located on the opposite side of the globe [2]. Crossing this line results in a date change of exactly one day. Although it generally follows the 180 meridian, the IDL deviates or 'curves' at specific locations, such as the Bering Strait and various island groups like Tonga, to ensure that political entities or island chains maintain the same calendar day and avoid administrative confusion. In contrast, the Equator and the Tropic of Cancer are lines of latitude, measuring 0 and 23.5 N respectively, and do not correspond to the 180 longitudinal measurement [1].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 18: Latitudes and Longitudes > 18.3. Comparison: Latitude vs. Longitude > p. 250
2. [2] Exploring Society:India and Beyond. Social Science-Class VI . NCERT(Revised ed 2025) > Chapter 1: Locating Places on the Earth > Before we move on ... > p. 24