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TopoQuest Frequently Asked Questions

Questions and Answers:

Q: Where did the map data for TopoQuest come from?
A: Recently, the Libre Map Project joined forces with the Internet Archive to make all USGS 1:24K scale DRG's (digital scanned topographic maps) available for free download.  TopoQuest obtained about 90% of the DRG files covering the continental US from the Internet Archive.  Some holes exist in the map coverage in the Libre Map Project, and some of the DRG files in the project have incorrect registration (particularly those tagged as referenced to the NAD83 datum), so the balance have been painstakingly obtained or downloaded from other sources.  Canadian topographic maps were obtained from Natural Resources Canada.  The 1:100K and 1:250K topographic maps and 1m satellite/aerial imagery covering the US came directly from the USGS.

Q: I have some Topozone map URL's that no longer work after Topozone was bought out by Trails.com.  What can I do?
A: The disappearance of Topozone was the main reason TopoQuest now exists!  To help former Topozone users out, you can replace topozone.com with topoquest.com in your old Topozone map URL's and leave the rest of the URL the same.  More details on converting your Topozone URL's to the TopoQuest equivalent is on our Topozone Replacement page.

Q: What's a DRG?
A: A DRG file is a scanned digital version of a USGS topographic map.  It is actually a TIFF image file that can be opened in any digital imaging or photo viewing software that can open TIFF files (.tif, .tiff) to view the map just as you would a real-world paper version of the topographic map.  Some additional information tags have been included in the TIFF file when the USGS created it to help mapping programs figure out what the actual location represented by that file is.  These additional tags, combined with the digital scanned map, are often referred to as a GeoTIFF file.

Q: What types of maps are contained in DRG files?
A: Any type of map can be represented by a DRG file, but in particular, the USGS has released the 1:24K, 1:100K and 1:250K series topographic maps in DRG form.  These are the three map scales that we're trying to make available on the TopoQuest website.

Q: Is it legal to copy and distribute DRG files?
A: In the case of USGS-derived DRG files, yes.  The USGS has released all topographic maps of the United States into the public domain, including the digital versions (DRG's).  It is legal to copy and distribute these files as you wish.  What may be confusing is that many vendors charge exorbitant fees to sell you a set of CD's or DVD's containing DRG files for a large area (typically a full state), but what they're charging for is the cost to distribute those files to you, rather than the data itself.  Additional information about the USGS's position on copyrighted data and the public domain status of USGS topographic maps can be found here.

Q: Why does this site exist?
A: Anyone that has tried to obtain digital topo maps (DRG's) for various uses, be it to use with a mapping program, to modify for personal use with new trails and markings, or just for the niftiness of having maps in digital form, has probably run into a major problem in obtaining DRG files.  It's hard to find them for free or at a reasonable cost!  It's typical for online vendors to charge many dollars per single DRG map file, or to charge upwards of $100 to sell you a set of CD's with the DRG map files for your state.  TopoQuest has three goals:  1) To make it inexpensive to find and download the few DRG files you might want or need.  2) To help you find the maps you want, through our search features and by browsing maps with our Map Viewer.  3) To let you browse topographic maps online in our Map Viewer, without having to download DRG files or a mapping program to view them.  Other information about how TopoQuest came to exist can be found on our About TopoQuest page.

Q: Aren't there other online mapping sites already that I can use to view topographic maps?
A: There are, though with the disappearance of Topozone (details on our Topozone Replacement page), the options are more limited.  Why did I create the Map Viewer portion of this site?  Well, mainly just for the fun and challenge of it, and I was greatly inconvenienced by Topozone being bought out by Trails.com!  I intended to reproduce the functionality Topozone used to have as closely as possible.  It gave me some creative time with PHP and MySQL to just mess around making something cool and interesting, as opposed to my real job where business sense and viability matters!  There's cases where TopoZone or TerraServer are what you're after, but there's also times that our own TopoQuest Map Viewer will fit the bill better, especially if you want to immediately download a DRG file of the map you're viewing.

Q: Where can I find more info about DRG files?
A: Try the USGS's DRG Info site.

Q: Where can I find a program to view DRG files?
A: You can use any program that can open a TIFF format image file.  If you want a program that can understand the GeoTIFF tags that specify where on earth the map file is referenced to, you can try the USGS's DLGV32 program.  Some commercial mapping software aimed at recreational users include Fugawi.

Q: I want to write a program that can load or manipulate DRG (GeoTIFF) files, where can I find some code?
A: You probably want to look at remotesensing.org's GeoTIFF resources page, which includes specifications of the GeoTIFF format, and libgeotiff, a C library for reading and manipulating GeoTIFF tags in GeoTIFF files.

Q: What datum is used on USGS DRG files?
A: USGS DRG topo map files tend to use the NAD27 datum, the same as that used on the actual paper maps.  Note that if you use coordinates read off a topographic map with your GPS, you may want to make sure you're using the same datum as the map.  Most GPS's default to NAD83 (or WGS84, which is the same) datum.  You can change the datum of the coordinates displayed in the Map Viewer by selecting the desired datum from the sidebar.

Q: Is it really free to download maps from TopoQuest?
A: Indeed.  Note that many of the download links point to the Libre Map Project files, while others point to our own copies of DRG's in cases where the Libre Map Project was missing files or the DRG's in the project contain coordinate registration errors.

Q: Why would you really do this for free?  Are you nuts?
A: Absolutely!  And because it was there to be done..  Later update: I've been experimenting with small banner ads on the site to help fund the massive hardware requirements needed to keep TopoQuest going!  The new 1m satellite/aerial imagery is sucking up huge amounts of disk space.


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