Latilongs are mapping units formed by successive lines of latitude and longitude, each at one degree intervals. These lines form a rectangular grid pattern across the state. Each latilong is assigned a number: 1 through 49 (Figure 1). Latilongs 48 and 49 cover small portions of southwestern Montana. The average dimension of each latilong is 47 miles (76 km) wide and 69 miles (111 km) long, representing an average area of 3,200 square miles (8,4326 km). Latilongs along the Canadian border are 5.4 percent smaller than those along the Wyoming border.

Quarter latilongs are created by dividing each latilong unit into four quarters (an area equivalent to that covered by sixteen 1:24,000 scale topographic maps).

Quarter/quarter latilongs are grid cells representing 1/4 of a degree of latitude by 1/4 degree of longitude (an area equivalent to that covered by four 1:24,000 scale topographic maps).