ABOUT 15 MINUTE MAPS
Maps in the 15 Minute Quadrangle series were made in the period between the 1890s and the 1950s. They were created by the Map Division of the United States Geological Survey (USGS). The purpose for developing this series was to provide a detailed topographic map coverage of the entire United States at the same scale. The series was gradually replaced by the 7.5 Minute Quadrangle series. Alaska is the only current area for which 15 Minute maps are still being produced. The 15 Minute Quadrangle maps provide vital geographic, historical, and topographic information that can be used in understanding the nature of a place.
The term “Quadrangle” is used to describe this series since the sides of the maps are 15 minutes of latitude and longitude in length. If one of these maps was produced at the equator, it would appear to be square in shape. The maps would take on more of a rectangular shape for areas away from the equator. However, with respect to distance of latitude and longitude the maps cover square areas, which resulted in the use of the term “Quadrangle.”
These maps are also called the 62,500 series. The number 62,500 refers to the fractional scale used on the map. It appears as 1:62500, which means one unit of distance used on the map is equal to the same unit of distance on the Earth. For example, one inch on the map relates to 62,500 inches on the ground. The map user selects the unit of distance; thus, a fractional scale generally does not indicate a unit of distance. A few maps in the series have a scale of 1:63,360. At this scale one inch on the map equals 63,360 inches or one mile on the ground. The fractional scale is good for measuring precise distances but if the physical size of the map was changed, this scale would no longer be correct. The maps also have a bar (sometimes called a “graphic”) scale. This scale is generally shown in miles and kilometers. This scale holds true if the map size is changed but it is harder to use in obtaining precise distance measurements.
The USGS was established in 1879 by consolidating various federal surveys involved in exploring western United States. In 1881, John Wesley Powell became director of the USGS. Powell fought for intelligent and scientific planning of the nation’s resources. He appointed Henry Gannett as the Chief Geographer of the USGS. In 1882, Powell and Gannett initiated a bold endeavor to map the entire nation at the scales of 1:125,000 and 1:62,500.
In 1888, the USGS started the process of mapping New York at the scale of 1:62:500. The first maps were made of the area around New York City. Between 1888 and 1891, 4,159 square miles of the State had been mapped, concentrating mainly in New York City and the lower Hudson Valley. By the early 1900s sixty four percent of the State was mapped and by the late 1920s all 54,556 square miles of the State were mapped.
In the late 1800s, topographic maps were made in the field by using tape and compass traverses of a series of points in order to determine the planometric accuracy of a surface. Aneroid barometers were used to calculate elevations. This information was incorporated into a process known as field sketching, the drawing of a terrain representation using contours. Later planetables and alidades were employed to measure elevations more rapidly and with greater accuracy. This entire process of field mapping took a great amount of time and was labor intense. In the 1930s aerial photography and photogrammetric techniques were developed as a means for measuring elevations. This process reduced considerably the time used in field mapping. In general, the maps in the New York collection that were produced before the 1940s were created through field sketching and mapping. The maps produced after the 1940s were based on aerial photography. Many of the maps in the collection have editions created on both field sketching and aerial photography.
Originally the maps in this series used black ink to indicate human landscape features and text, brown ink for topographic lines called contours, and blue for water and wetland surfaces. Beginning in the 1910s green ink was added to illustrate natural vegetation coverage. Finally in the 1920s red ink was introduced to show roads and marginal information about distance and direction to the next city on the adjacent map.Over the years most of the maps in the collection have faded with respect to their background colors.
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