The latest in the free, useful tools from Metzger & Willard. -- QUADS (http://www.metzgerwillard.us/quads/) is a web-based service for visualizing USGS quadrangles in Google Earth that provides an easy-to-use framework for retrieving georeferenced PDF topo maps from the USGS Store.

This article first appeared in the October, 2009 edition of The American Surveyor Magazine 

QUADS also includes USGS, or USGSderived, overlays for grayscale and color shaded relief maps, topographic-bathymetric maps, black-and-white orthophotos, and urban areas color orthoimagery.

QUADS
The principal component of QUADS is a Google Earth network link (Google 2009) that plots the approximate boundaries of more than 59,000 USGS quadrangles (Figure 1). For each of these quadrangles, GeoPDF maps (TerraGo 2008, USGS 2008a) may be freely obtained from the USGS Store (USGS 2008f). All quadrangle balloons (Figure 2) contain name, state, extent, and date information with a link to the corresponding GeoPDF map. See also USGS (2008e) for a discussion of various map series and USGS (2008d) for a list of topographic map symbols.

Quadrangles are categorized by extent and collected in subfolders. Coverage includes the conterminous United States, Alaska, Hawaii, Puerto Rico, the US Virgin Islands, and portions of Antarctica. The user is prompted to zoom in if there are more than 500 quadrangles in view. If there are no quadrangles within the viewer bounding box, the Search Results network link will contain an empty folder named OutOfRange.

GeoPDFs were initially produced by the US Army Corps of Engineers Topographic Engineering Center (currently known as the US Army Geospatial Center) using Digital Raster Graphics (DRGs) with a resolution of 250 pixels per inch (ppi). GeoPDFs produced by the USGS are created from high-resolution (up to 508 ppi) scans of paper maps. The quadrangle balloon GeoPDF download link is preceded by either the designation DRG or MAP to indicate Corpsproduced files or USGS-produced files, respectively. File sizes range from 3 to 30 megabytes, most being on the order of 10 to 17 megabytes.

The USGS is engaged in an ongoing effort to scan all existing maps, including historical map versions, and has recently introduced the new Digital Map series (USGS 2009b). The QUADS database will be updated periodically to reflect changes in the USGS map offering.

QUADS is similar in function to the Map Locator (USGS 2008c), a Google Maps application that runs in the user's web browser. The Locator is an outstanding browser application but lacks the robust user interface and flexibility of Google Earth 

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A 1.595Mb PDF of this article as it appeared in the magazine—complete with images and live links—is available by clicking HERE