The alternate name for contour lines is option 3, Isohypse. Contour lines are used to represent areas of equal elevation on a map or a topographic representation. They connect points of the same elevation and form a continuous line. Isohypse is derived from the Greek word "iso," meaning equal, and "hypse," meaning height or elevation.

Option 1, Isopotential, is not the correct answer in this context. Isopotential refers to areas of equal potential, which is typically used in the field of physics or electrical engineering.

Option 2, Istherm, is also incorrect. Istherm refers to lines on a map that connect points of equal temperature, typically used in meteorology.

Option 4, Isohyet, is not the correct answer either. Isohyet refers to lines on a map that connect points of equal precipitation, typically used in climatology or hydrology.

Therefore, the correct alternate name for contour lines is option 3, Isohypse.