This metadata file applies to the overall collection. The individual RCCs are accompanied by their original USGS metadata.
This is a file collection of USGS Raster Color Composite (RCC) GeoTIFF images. They are georeferenced images of USGS topographic maps, from the DRG (digital raster graphic) family of USGS products, essentially the same as DRGs but at a higher resolution. See the supplemental information section for more about RCCs.
Resolution is 500 and 1000 dots per inch (dpi). The spatial reference is UTM zone 15 or 16, NAD 1927 or 1983, as appropriate to the individual map images. The collection includes about 75 7.5-minute quadrangles in Illinois that have been obtained for recent geologic mapping efforts.
The majority of the files show the entire topotraphic map. Some, however, show only the text layer. The majority are archived "as delivered", but a handful have been subsequently processed to add a blue fill for water bodies.
Any combination of "as delivered" files with the following extensions may accompany the RCC GeoTIFFs: .dat - a list of parameters about the image, .fgd - the USGS metadata file, .tfw - the TIFF world file. The image files also have related ESRI ArcGIS files such as .rrd and .aux.
Naming convention: The files are named according to the traditional USGS quadrangle convention, e.g. 37088d8.tif. Files with 1000 dpi resolution have "1000" appended to the file name, e.g. 37088d8_1000.tif. Files that have an added color fill for water bodies have the letter "f" appended to the file name, e.g. 37088d8f.tif.
Note that the bounding coordinates reported below are for the entire state of Illinois, not for any single quadrangle.
rcc = Raster Color Composite. DRGs at 500 and 1000 dpi. rcs = Raster Color Separate. With collar information removed rfs = Raster Feature Separate. Conform to a draft archive standard.
Traditional analog feature separates
The original materials for a USGS 7.5-minute quadrangle are various types of mylar negatives. Most of these materials are scribecoats -- mylar sheets coated with a thin layer of wax. During original map compilation the wax was scraped off with precision scribing instruments, producing what is essentially a hand-crafted negative.
The organization of these materials was driven first by the 7.5-minute format of the maps, and second by the color characteristics of the quadrangles. Traditional USGS maps are printed with five colors of ink (black, red, brown, green, blue). The white paper makes a sixth color, and purple was added in the 1960s as a seventh. Six additional colors are typically simulated with lithographic screens.
All the features on one feature separate are of the same color, but not all features of the same color are on one separate. Over the years conventions and production guidelines were developed for what features should be grouped together on a separate, but these relationships were never formally standardized. The average quadrangle has about eight feature separates, but it is not unusual for there to be as many as 20.
The mylar separates are saved in USGS archives for every topographic quadrangle. Although the mylar is fairly durable, it does not last forever. As quads are reprinted and revised, the mylar sheets are refreshed by photographic copying. Unfortunately, each generation of copying degrades the image quality slightly. Some layers of some quadrangles are on their sixth or seventh generation, with visible deterioration in the linework.
Digital feature separates
Starting in the early 1990's, digital drafting tools began to replace scribing in map revision. A map revision typically begins with scanning the feature separates of the old map. The resulting digital separates are updated in computer aided drafting (CAD) environments. The primary outputs of the revision are digital feature separates that can be combined to make press negatives to print a new map, or a digital composite that can be used to make a digital raster graphic (DRG).
The USGS has always sold copies of the mylar feature separates, and there is now a growing demand for digital feature separates. Even if this were not true, there is still a need to standardize the format, packaging, and archive methods of digital feature separates to ensure that data produced today can still be found and read the next time they are needed.
The DRG images were made by combining the RFS files. They are standard USGS DRGs, except that (1) the scan resolution is 1000 dpi instead of 500 dpi and (2) no FGDC metadata files are present.
The RFS images will display as black-and-white positives. The physical file format is very close to that of DRGs. The images conform to TIFF 6.0 and GeoTIFF 1.0. They are 8-bit palette color images with PackBits compression. Most of the same TIFF tags and GeoTIFF keys that are populated for DRGs are also populated for these RFS.
The image quality of a RFS is always better than that of a DRG made by scanning a paper map. Scanning mylar materials at 1000 dpi always produces a sharper image than scanning paper at any resolution. Nevertheless, there will still be significant variation in the quality of RFS, depending on the condition of the source materials.
Links to these are provided in the Cross References section.
Individuals or entities may make fair use of copyrighted ISGS material, such as reproducing a single figure or table, or using a brief text quotation, without obtaining formal permission, but in all cases the Illinois State Geological Survey must be credited as the source of the material. To reproduce ISGS information beyond the fair use standard, permission must be obtained from the ISGS Information Office, 615 East Peabody Drive, Champaign, Illinois 61820, 217-333-4747, email@example.com. License fees and a license agreement may be required, depending on the proposed usage.
Map information is to be used at a scientifically and cartographically appropriate scale, that is, at a scale no greater than indicated on the map or as described in the documentation of the map or map data. Map information is not appropriate for, and is not to be used as, a geodetic, legal, or engineering base. Map information has no legal basis in the definition of boundaries or property lines and is not intended as a substitute for surveyed locations such as can be determined by a registered Public Land Surveyor.
The data do not replace the need for detailed site-specific studies.
Some files were named with a "g" or "geo" at the end of the file name. The meaning of these designations is unknown and they were removed from the file name. If there were duplicate files for a given quad only the file with the most recent date was retained.
Two files had undefined projections (o38089f8_1000.tif and o37089g5_1000.tif.) The projections were defined to be that shown on the map image.
Raster pyramids (.rrd) were added in ArcCatalog with the Batch Build Pyramids tool. This also added the .aux files.
Some files were named with "geo" at the end of the file name. The meaning of this designation is unknown and it was removed from the file name.
Raster pyramids (.rrd) and .aux files were added using ArcCatalog.
Each raster entity or pixel contains a color index from 0 through 12 referencing a color palette of RGB values from 0 through 255 in which the standard colors used in the DRG are defined.
USGS DRG Color Palette Digital Number Color Red Green Blue 0 Black 0 0 0 1 White 255 255 255 2 Blue 0 151 164 3 Red 203 0 23 4 Brown 131 66 37 5 Green 201 234 157 6 Purple 137 51 128 7 Yellow 255 234 0 8 Light Blue 167 226 226 9 Light Red 255 184 184 10 Light Purple 218 179 214 11 Light Grey 209 209 209 12 Light Brown 207 164 142
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Illinois Natural Resources Geospatial Data ClearinghouseGenerated by mp version 2.8.25 on Wed Apr 08 11:01:14 2009