The maps on these CD-ROM's make up an exceptionally detailed atlas of United States topography. They have been computed from the U.S.G.S. 3 arc second digital elevation database. Height above sea level is indicated by continuous color variation and relief is indicated by shading produced by a westerly artificial light source.
On CD-ROM the maps for each state are located in a separate folder. Within each of these state folders there is a screen-sized map of the entire state together with the collection of all one-by-one degree (in latitude and longitude) quadrangles of which the state is composed. The latter are cropped to state boundaries and their icons on the desktop are arranged in the shape of the state they represent for easy reference. The one-by-one degree map files are designated by the latitude and longitude of their southeast corners and their scale is approximately 1:530,000.
The digital maps in this collection are easily edited in any paint or imaging software that reads graphics in PICT format for Macintosh platforms or TIFF in the PC environment. In addition, because the one-by-one degree quadrangles are in 24 bit color, they can be tiled together into larger maps in applications such as Adobe's Photoshop. On a screen with a pixel density of 72 dpi, each quadrangle measures 8.33 by 8.33 inches. Thus, for example, when the state of Texas, which is composed of 84 one-by-one degree tiles, is assembled into a single map at 1:530,000 it measures approximately 115 by 95 inches on a virtual screen. Such large scale maps can be output to a printer capable of handling files of that size. Experience suggests that, when map size is reduced by about 65% and pixel density is correspondingly increased to 110 pixels per inch, output to high quality printers such as the Iris 3047 shows no evidence of pixel structure.
The one-by-one degree quadrangles on these CD-ROM's should be usable in any GIS application that accepts PICT (Mac) or TIFF (PC) graphics and permits the user to register at least the northwest and southeast corners. All of these quadrangles are computed in geographic coordinates so that individual pixels are spaced on a regular grid of 6 seconds in latitude and longitude, giving a pixel resolution of 500 feet. Where projections such as Lambert are desired, changing the map's ratio of width to height corresponding to latitude will produce a close approximation.
Users are free to reproduce maps on U.S. Digital Topography for a wide variety of applications. There are restrictions on reproduction of images in atlases, CD-ROM products, broadcasting, group publishing, cartographic services and reuse within other clip-art products. Please review the license agreement and contact Digital Wisdom Inc. for details where your use may potentially conflict with the license.
The CD-ROM’s are available as follows:
States East of the Mississippi and TX, LA & HI Macintosh PICT only
States West of the Mississippi excl TX, LA & HI Macintosh PICT only
