What are the types of grid reference?

Grid references are typically categorized into two main types: four-figure and six-figure references. A four-figure grid reference identifies a specific area within a grid square, using two digits for the easting and two for the northing. A six-figure grid reference provides a more precise location within that square, including three digits for the easting and three for the northing. Additionally, there are lettered grid references used in some mapping systems, which combine letters for location identification.