Isohaline is an imaginary line joining the places having equal :

An isohaline is defined as an imaginary line or contour on a map that connects points or places having equal salinity [c4][t1]. In oceanography and estuarine studies, these lines are used to visualize the distribution of salt concentration and the degree of mixing between freshwater and saltwater [t1][t2]. Salinity is typically measured in parts per thousand (ppt), with the average ocean salinity being approximately 35 ppt [c4][t5]. While other terms describe lines of equal atmospheric or solar properties—such as 'isobars' for pressure or 'isotherms' for temperature—'isohaline' specifically refers to salt content [t8]. In contrast, 'insolation' refers to incoming solar radiation received by the Earth, which is measured as energy per unit area rather than salinity [c1][c2]. Therefore, isohalines are essential tools for mapping the chemical properties of oceanic and estuarine water bodies [t1].

Sources

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 12: The Oceans > Salinity of the Ocean > p. 107
2. [2] https://oceanservice.noaa.gov/education/tutorial_estuaries/est05_circulation.html
3. [3] https://www.epa.gov/sites/default/files/documents/sfep_1993_managing_fw_discharge_sf_bay_delta_estuary_0.pdf
4. [4] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 21: Horizontal Distribution of Temperature > Insolation > p. 282
5. [5] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 33: Ocean temperature and salinity > Factors Affecting Temperature Distribution of Oceans > p. 511