One of the most popular maps of the United States Geologic Survey (USGS) is the 7.5-minute quadrangle map. Produced at a scale of 1:24,000, each of these maps covers a four-sided area of 7.5 minutes latitude and 7.5 minutes longitude. The United States has been divided into precisely measured quadrangles. Each quadrangle in a state has a unique name. The maps of adjacent quadrangles may be combined to form a large map. There are more than 54,000 USGS topographic maps that cover the 48 contiguous states and Hawaii.