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The Library of Congress National Digital Library Program and the
Geography and Map Division announce collection number eighty-three at
the American Memory online collections Web site:

”The American Revolution and Its Era: Maps and Charts of North America
and the West Indies, 1750-1789” at:
http://memory.loc.gov/ammem/gmdhtml/armhtml/armhome.html

The collection presents an important historical record of the mapping of
North America and the Caribbean online. Advancements in mapmaking tools
and the onset of the French and Indian War and, later, the American
Revolution, created a flurry of activity in European and North American
mapmaking and publishing. This online collection will include well over
two thousand different maps and manuscripts, with easily as many or more
unnumbered copies, many with distinct colorations and annotations. Over
the next several years many of the maps and charts in this bibliography
will be added to the online collection each month. At this time,
approximately 100 maps are being released.

Almost six hundred of the items in this collection are original
manuscript drawings, a large number of which are the work of such famous
mapmakers as John Montresor, Samuel Holland, Claude Joseph Sauthier,
John Hills and William Gerard De Brahm.. Historical cartographers can
compare multiple editions, states, and impressions of several of the
most important maps of the period, follow the development of a
particular map from the manuscript sketch to the finished printed
version and its foreign derivatives, and examine the cartographic styles
and techniques of surveyors and mapmakers from six different countries
Great Britain, France, Germany, Spain, Holland, Italy, and the United States.

Most of the items presented here are documented in “Maps and Charts of
North America and the West Indies, 1750-1789: A Guide to the Collections
in the Library of Congress”. The online essay ”Mapping the American
Revolution and Its Era” is taken from this bibliography.

Map specifications and scanning
The digital images were created by staff in the Geography and Map
Division by scanning the original map on a large-format (24 x 34 inches)
flatbed scanner using RGB (red- green-blue) color separation. The
scanner was loaned to the Division by Tangent Color Systems. Each
raster image was produced by scanning the item at a resolution of 300
dots- per-inch and converting the resulting proprietary file format to
TIFF format. These TIFF files, which average approximately 180Mb, are
moved over a network to Surestore jukebox 1.3Gb magnetic optical
platters for temporarily offline storage. The Surestore jukebox and the
associated servers and workstations were donated by the Hewlett Packard Company.

Following scanning, the TIFF files were enhanced using the WindowsNT
version of xRes, an image processing software, to rotate, crop, adjust
brightness or contrast, and stitch together TIFF images for items
requiring multiple scans. This software was donated by Macromedia. The
TIFF files were compressed, using a wavelet-based image compressing
software called Multi-Resolution Seamless Image Database, or MrSID. The
final step was the creation of a small GIF file for use as the initial
thumbnail display of the item. After completing the scanning, the
Archive TIFF file along with the SID and GIF files are stored on the
Library's RS6000 World Wide Web server.

Specifications:
Master image: Scanning resolution: 300 dpi. Tonal resolution: 24 bit
color, RGB separation. File format: TIFF. Compression: none

Reference image: Scanning resolution: 300 dpi. Tonal resolution: 24
bit color, RGB separation. File format: SID. Compression: Wavelet

Thumbnail image: Viewing resolution: 72 dpi. Tonal resolution: 8 bit
color, RGB separation. File format: GIF. Compression:none

Map files delivery
The Library's world-wide-web delivery of very large digital files of
maps is accomplished by using a wavelet compression technology made
available to the Library of Congress by LizardTech of Seattle,
Washington. The multiresolution seamless image database --MrSID--
software for the storage and retrieval of large digital images is
derived from the research efforts of Los Alamos National Laboratory, New
Mexico. In contrast to other compression software that relies on
tiling, MrSID gets all its sharp resolution from within a single
compressed image, and it does not require any special hardware. File
size does not matter. MrSID allows immediate access to any part of an
image, of any size, at any resolution. This software integrates
multiple resolutions of an image in a single file which enables Internet
users to zoom in, getting more and more detail.

Although MrSID is a "lossy" compressor, the images were compressed at a
ratio of 22:1, depending on image content and color depth, without
experiencing any loss of information. Because fast easy access is
provided via networks and the Internet to vast amounts of geographic
information, MrSID is ideal for viewing maps, or photos, terrain models,
and satellite data.

Please direct any questions about this collection to [log in to unmask]


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