What type of chart shows the variation in magnetic declination?

An isogonic chart is specifically designed to illustrate variations in magnetic declination across different geographic areas. Magnetic declination, or magnetic variation, refers to the angle between magnetic north (the direction the north end of a magnetic compass points) and true north (the direction along the Earth's surface towards the geographic North Pole).

Isogonic charts feature contour lines known as isogons, which connect points of equal magnetic declination. This allows surveyors and navigators to understand how the magnetic field varies in a region, which is crucial for accurate navigation and mapping.

In contrast, topographic maps focus on representing the physical features of the terrain, such as elevation and landform shapes. Bathymetric charts depict underwater topography, showing the contours of the sea floor. Weather maps are utilized to display meteorological conditions and patterns, including temperature, precipitation, and wind. None of these map types provide the specific information about magnetic declination that isogonic charts do.