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Map Tile – USGS Quadrangles

Early US Geographical Survey maps used lines of longitude and latitude as tile boundaries. The four-sided figure that you get when you do this is not a rectangle (lines of longitude are not parallel) so they came up with the term “quadrangle”. Because the concept is easy to understand and has been around for a long time, it has become the standard for many geospatial data products. The US Geological Survey uses the concept of “quadrangles” to organize it’s paper and digital products.

One-Degree Blocks

One-degree blocks are the rectangular areas on the earth’s surface formed by the lines of latitude (running east and west) and the lines of longitude (running north and south). One-degree block names consist of the latitude of the south boundary of the block and the longitude of the east boundary of the block. UWGB falls into the block bounded by 44 degrees on the south, 45 degrees on the north, 87 degrees on the east and 88 degrees on the west. The block name is 44087

24k Quadrangles

The 1:24,000 scale topographic maps published by USGS are an important and frequently used map series. 24k topos employ a tiling scheme based on dividing the earth in to one-degree blocks and then dividing each block into 8 rows and 8 columns of equal-size tiles. Since one-eighth degree = 7½ minutes, the tiles are often referred to as “7½ minute quadrangles”. Each“quad” has a locally significant name – “Laughing Fish Point” and “Lake Lucerne” are some examples from our neck of the woods. The UW-Green Bay campus falls entirely within the Green Bay East quadrangle which is defined as follows.
        South to north extent: 44° 30′ to 44° 37½’ north
        East to west extent: 87° 52½’ to 88° 0′ west

USGS also assigns an alphanumeric ID code to each 24k quad. The code consists of the 5-digit block name plus a two character code that identifies the quadrangle’s position in the one-degree block. Because the ID code works better for computer searches, it has become an important tool for organizing spatial data. To completely define UWGB’s quadrangle one would have to furnish the following information.
        Quadrangle name: Green Bay East
        Quadrangle id: 44087e8

A list of the 24k quadrangles intersected by a project footprint is essential project planning information.

100k Quadrangles

The 1:100,000 scale maps published by USGS are an important component of their small-scale map offerings. The 100k map series employ quadrangles that span one degree of longitude and one-half degree of latitude on a single sheet.

250k Quadrangles

The 1:250,000 scale maps published by USGS are an important component of their small-scale map offerings. The 250k map series employ quadrangles that span 2 degrees of longitude and one degree of latitude on a single sheet.

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