TopoQuest

TopoQuest is a free topographic mapping website that offers free online map viewing and downloads of USGS topographic maps, similar to Microsoft's TerraServer-USA and the former TopoZone.

History
TopoQuest was originally created in July 2001 as an experiment in combining Linux, PHP and MySQL to facilitate easy access to USGS topographic maps viewable online. The increasing popularity of Demand Media's TopoZone, another online mapping website with similar features, resulted in shelving the TopoQuest source code after the initial proof of concept.

On April 9, 2008, Demand Media's TopoZone website became a subscription-only website when it was incorporated into Demand Media's Hillclimb Media subsidiary Trails.com. Outside links to TopoZone maps now access limited map viewing capabilities, leaving many Internet users unable to find or access the topographic maps they seek . In response, the previously developed TopoQuest source code was unshelved on April 10, 2008 to build a free replacement for TopoZone with similar features.

Map Source Data
The source data for TopoQuest's maps comes from the Libre Map Project. Libre Map Project is a full collection of 1:24K scale USGS topographic maps in Digital raster graphic format hosted by archive.org . TopoQuest downloads the raw Digital raster graphic map files and preprocesses them into large map "tiles" that the map viewer on the website uses to generate each map view. The DRG topographic map files are rescaled to 4 meters per pixel resolution, adjusted for consistent map projection, and tiled into 512 x 512 pixel pieces that the map viewer assembles individual map views from. Additional map tiles are then generated at 8, 16, 32 and 64 meters per pixel. The maps are then dithered and normalized to an adaptive set of 64 colors to allow any 4 intersections of maps to fit within the 256 colors available in the GIF image format. The University of Minnesota MapServer software is used to dynamically generate the map views that users navigate on the site. The project relies heavily on GDAL to process and tile the images files into their final form.

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