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On-line Digital Data Formats
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USGS digital geologic maps are available in several formats. Most maps come with text pamphlets that discuss the geology shown on the map and the details of the digital nature of the maps. The text pamphlets are also available in several formats. The formats of the maps and texts are described below:

Text-only: These files are unformatted text files (No bold, italic, underlined, or otherwise made fancy text). These files are included because they can be read by every computer, word processor, web browser, everything. However, because they are unformatted, they can be hard to read. We suggest that if you can use a different format for the texts, you do. There are no text-only maps.

PDF: These files are produced and read by a program called Adobe Acrobat. Adobe gives the software necessary to view and print the files away FREE at their website ( You will have to get the software before you can use the PDF files. However PDF files contain formatted texts and full color map sheets. They can be viewed on screen dynamically (you can zoom in and pan around, important for maps) or printed (see helpful hints below). PDF files are the best choice for most users. For more help with PDF files, please click here.

PostScript: This is the format most printers and plotters use. This format can also be used by high-end graphics software like Adobe Illustrator. For most users, PDF files are a much better choice because PostScript files can be as much as 50 times larger and because many users don't have the high-end software or large format plotters to use PostScript files. However, PostScript provides an improvement in print quality. So, if all you want to do is print a text pamphlet on a laser printer, PostScript files are best.

JPEG: This is a standard image format for the Internet. These files are simple pictures of the maps. Users cannot zoom in, so they are not as useful as PDF files. But, they load quickly right onto your screen. If all you want is a quick look, JPEG files are for you.

Tarfiles: Tarfiles are archives of two or more plotfiles, databases, and text-only files. The tarfiles are very large, and contain the technical data used to make the geologic maps. Unless you use a Geographic Information System database package like ArcView or ARC/INFO, these files are not for you. If you do use GIS, please refer to the detailed explanation of the data structure given in the database explanation pamphlet (ReadMe), available as text-only, PostScript, and PDF.

Helpful Hints-

If you want PDF files, download them to your hard-disk:
PDF files, especially maps, work much faster and better when the PDF file is on your hard-disk. They can be viewed via the Internet using the PDF Reader Plug-In, but this tends to be slow. Reading PDF files of text pamphlets via the Internet does not pose as much of a problem. Nevertheless, it is probably best to download all PDF files to your hard-disk.

On most computer/browser combinations, downloading to the hard-disk involves pointing at the link to the PDF file (the underlined colored writing), using the right mouse button and selecting "Save Link As" or something like that. If you only have a one-button mouse, try holding down the "Option" key while you click on the link (that works for Netscape on a Mac).

However, some computer/browser combinations may not have that option. In that case, to download PDF files to your disk, open up your Preferences menu, go to where your browser Plug-Ins are controlled, and turn off the PDF-Reader plug in. For example, on a Netscape browser running on a Mac, choose Helpers on the Preferences Menu, click on Portable Document Files, click on Edit, and click on Save to Disk. Different computer/browser combinations will have different procedures, but the idea is to turn off the software (plug-in) that is trying to draw the PDF on screen in your browser, and to tell the browser to save the file to your hard-disk.

Of course, if you never installed the PDF-Reader plug in, you don't have to worry about this, but many browsers these days come with it pre-installed. If you click on the link and you get a Save option, you are ok. If it starts to draw, click on Stop, and turn off the plug in.

How to print part of a geologic map on an 8.5 x 11 inch printer:
Although the Adobe Acrobat software available for free does allow users to print PDF files, most maps are formatted for a single large page (36 X 44 inches or so). Most users don't have the large format plotters required to print the whole thing, and unfortunately Acrobat doesn't allow you to choose which part to print, you get the upper-left hand corner.

There is an easy way to get the part you want, however. Zoom in until the area you want fills the Acrobat window. It is important to zoom in as much as you can now. Then use the select graphics tool to select the whole screen. Then use the copy tool. This converts what is on the screen to a bit-mapped image on your clipboard (or equivalent). The image can be pasted into almost any program that allows images, including most word processors. The image can then be printed using the new program. The bit-mapped image isn't quite as crisp as the original, but it is pretty good. Don't try to make the bit-mapped image larger once you have pasted it though, those pixels get large fast! That is why it was important to make the image as big as you could before you copied it. We have successfully completed this operation with both a Mac and a Windows machine.

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