The correct answer is option 4, latitude. Latitude refers to the distance of a location from the equator, and it plays a significant role in determining the intensity of insolation or incoming solar radiation. The amount of solar energy received at different latitudes varies due to the curvature of the Earth and the angle at which sunlight reaches the surface.

Option 1, altitude, also affects the intensity of insolation to some extent. Higher altitudes usually receive more intense sunlight because there is less atmosphere for the sunlight to pass through. However, the primary determinant of insolation intensity is latitude, not altitude.

Option 2, the nature of terrain, can locally influence the intensity of insolation. For example, mountains can create shadows and block the sun, while reflective surfaces like snow or sand can amplify the amount of solar radiation. However, this is a localized effect and not a general rule that applies universally.

Option 3, wind, does not directly affect the intensity of insolation. Wind is the movement of air caused by temperature differences, and it does not impact the amount of solar radiation reaching an area.

In conclusion, while altitude, nature of terrain, and wind can have some impact on the intensity of insolation, the primary factor is latitude.