LIBRARY : <NONE> LAYER NAME : <NONE> NAME : DRG - Digital Raster Graphic USGS 7.5' Quad Images (trimmed) LOCATION : /drg COVERAGE DESCRIPTION: Trimmed Digital Raster Graphics are PackBit-compressed tiff images of USGS 7.5 minute quadrangle maps that have been trimmmed down to their neat line, or in the case of irregular DRGs, to their outer map extent, removing the map collar that contains legends and descriptive text. This enables side by side display without map areas being overlapped by adjacent map collars. There are 2,851 images covering the entire state. Trimmed DRGs are directly derived from the full sheet DRGs that Teale Data Center scanned on behalf of the USGS. BRIEF METHODOLOGY: - Image is scanned at 400 dpi, and colors normalized to 13 RGB values. - Image is converted to Arc Info grid file - Grid file undergoes descreening to eliminate scatter and enhance solid fills in areas such as water bodies and forests. - Grid file is registered to albers projection. - Grid file is trimmed to its neatline or outer map extent. - Trimmed grid file is converted to .tif image with PackBit compression option. VITAL STATISTICS: Resolution: 400 d.p.i. Projection: Albers Units: Meters 1st Std. Parallel: 34 00 00 (34.0 degrees N) 2nd Std. Parallel: 40 30 00 (40.5 degrees N) Longitude of Origin: -120 00 00 (120.0 degrees W) Latitude of Origin: 00 00 00 (0.0 degrees) False Easting (X shift): 0 False Northing (Y shift): -4,000,000 Datum: NAD 27 Spheroid: Clarke 1866 Source: U.S.G.S. Source Media: Map sheets Source Projection: vary Source Units: Meters Source Scale: 1:24,000, 11 DRGs are 1:25,000 Capture Method: Scanned Conversion Software: ARC/INFO rev. 7.2.1 Data Structure: Raster Size of DRGs: Range 2 - 40 MB, 13 MB on average per image 40 Gigabytes statewide Use limitation: Value added product for purchaser's use only Data Updated: December 1998 FILE NAMES There are 64 DRGs in each 1 degree block of longitude and latitute, filling 8 rows and 8 columns. DRG files are named according to USGS 'ocode' designation: example: t35116a7.tif t denotes trimmed version of DRG 35 degree of latitude 116 degree of longitude a row (a-h south to north) 7 column (1-8 east to west) Some quad maps of islands and coastal areas are irregularly sized and/or positioned. File names for these images are determined by which quad their south east corner falls in. In three instances this creates a discrepancy with the USGS code: Filename Map Name USGS ocode o40124a2 SHUBRICK PEAK o40124b2 o33118f2 LONG BEACH o33118g2 o33118d8 SANTA BARBARA ISLAND o33119d1 TFW FILES Each DRG has an accompanying 'world' file with the same file name, but with a .tfw extension, that contains geo-referencing information: example: t35116a7.tfw 1.52786215012960 pixel size (meters) 0.00000000000000 rotation factor 0.00000000000000 rotation factor -1.52786215012960 pixel size 284543.57694197021192 image min x (meters) (NW -316411.17369714472443 image max y (meters) Corner) The min x and min y coordinates relate to the most upper left pixel in the image. Coordinates are in albers projection. COLORS Colors on the DRGs have been normalized to 13 RGB values: 0 0 0 black 255 255 255 white 91 159 230 dark blue 230 45 30 red 162 96 71 dark brown 210 255 177 green 197 101 197 dark magenta 255 240 0 yellow 202 225 245 light blue 255 202 197 light red 250 202 250 light magenta 230 230 230 light grey 222 167 146 light brown TRIMxx.DBF - dbase file that contains metadata for each quad on a CD. TRIMxx.DBF fields: COL ITEM NAME WDTH OPUT TYP N.DEC 1 FILENAME 8 8 C - 9 MAPNAME 30 30 C - 39 MAPNAME25 20 20 C - 59 CD 2 2 I - 61 FILESIZEMB 4 5 F 2 65 MAPSCALE 8 8 C - 73 FORMAT 20 20 C - 93 REF_CODE 25 25 C - 118 YEAR 4 4 C - 122 YRORIGMAP 4 4 C - 126 YRREVISION 4 4 C - 130 YRAIRPHOTO 4 4 C - 134 YRFIELDCK 4 4 C - 138 YRPHTOTOPO 4 4 C - 142 YRREVSOURC 4 4 C - 146 YRPHTOINSP 4 4 C - 150 SOUTH 8 10 F 5 158 NORTH 8 10 F 5 166 EAST 8 10 F 5 174 WEST 8 10 F 5 182 SE_COR_LON 9 9 C - 191 SE_COR_LAT 9 9 C - 200 CONTOURINT 10 10 C - 210 CONINTRMIT 10 10 C - 220 VERT_DATUM 15 15 C - 235 STATE1 2 2 C - 237 STATE2 2 2 C - 239 TYPE 1 1 C - 240 PROJECTION 80 80 C - 320 NOTES 175 175 C - FILENAME USGS coding convention for 7.5 X 7.5 minute quads. MAPNAME Name of 7.5 X 7.5 minute quad map MAPNAME25 Name of 7.5 X 15 minute quad map (see note below) CD CD number - index to which CD the image is on FILESIZEMB Size of tiff image file in megabytes MAPSCALE Scale of scanned map FORMAT Dimension in Minutes of map, N-S X E-W REF_CODE USGS reference code YEAR Most recent year that appears on the map. YRORIGMAP Year of original map YRREVISION Year of map revision YRAIRPHOTO Year of aerial photography used for revision YRFIELDCK Year of field check YRPHTOTOPO Year of aerial photography used for topography base YRREVSOURC Year of source data for revision YRPHTOINSP Year of photo inspection SOUTH Southern extent of map area, decimal degrees NORTH Northern extent of map area, decimal degrees EAST Eastern extent of map area, decimal degrees WEST Western extent of map area, decimal degrees SE_COR_LON Longitude at south-east corner, degrees minutes seconds SE_COR_LAT Latitude at south-east corner, degrees minutes seconds CONTOURINT Contour interval CONINTRMIT Intermittant contour interval VERT_DATUM Vertical Datum STATE1 State primarily covered in the image STATE2 State secondarily covered in the image TYPE Type of map, to identify non standard maps S Standard 7.5 X 7.5 Minute T Tall >7.5 X 7.5 Minute W Wide 7.5 X >7.5 Minute O Oversize >7.5 X >7.5 Minute 2 Double 7.5 X 15.0 Minute I Island vary PROJECTION Projection of map sheet NOTES Notations 1:25,000 SCALE 7.5' x 15' USGS TOPO MAPS 21 trimmed DRGs are derived from 1:25,000 scale 7.5' x 15' USGS topo maps. These DRGs have been trimmed to their 1:24,000 scale 7.5' X 7.5' neatline. These maps occur in portions of Trinity, Shasta and Tehama counties, and at one location on the California-Nevada border. FILENAME 1:24,000 MAP NAME 1:25,000 MAP NAME (trimmed from) t39119h8 SEVEN LAKES MOUNTAIN DOGSKIN MTN t40122a7 SOUTH YOLLA BOLLY MOUNTAINS SOUTH YOLLA BOLLY t40122a8 SOLOMON PEAK SOUTH YOLLA BOLLY t40122b7 TOMHEAD MOUNTAIN NORTH YOLLA BOLLY t40122b8 NORTH YOLLA BOLLY NORTH YOLLA BOLLY t40122c5 CHICKABALLY MTN EAST CHICKABALLY MTN t40122c6 CHICKABALLY MTN WEST CHICKABALLY MTN t40122c7 BEEGUM BEEGUM t40122c8 PLATINA BEEGUM t40122d5 ONO EAST ONO t40122d6 ONO WEST ONO t40122d7 ARBUCKLE MOUNTAIN CHANCHELULLA PEAK t40122d8 CHANCHELULLA PEAK CHANCHELULLA PEAK t40123a1 WRIGHTS RIDGE FOUR CORNERS ROCK t40123a2 FOUR CORNERS ROCK FOUR CORNERS ROCK t40123b1 BLACK ROCK MOUNTAIN BLACK ROCK MTN t40123b2 SWIM RIDGE BLACK ROCK MTN t40123c1 PONY BUCK PEAK PONY BUCK PEAK t40123c2 SMOKY CREEK PONY BUCK PEAK t40123d1 WILDWOOD DUBAKELLA MTN t40123d2 DUBAKELLA MOUNTAIN DUBAKELLA MTN 7 DRGs were scanned from quad maps that have NAD83 corners: t38121e3 CARMICHAEL t38121e6 DAVIS t38121e7 MERRITT t38121f3 CITRUS HTS t38121f4 RIO LINDA t38121g3 ROSEVILLE o38121h4 SHERIDAN These images have been shifted back to NAD27 position, and minor edits have been made to map features at the neat lines: DATAFILE NAME: DRGINDEX.PAT RECORD LENGTH: 70 COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ------------------------------------------------------------- 1 AREA 8 18 F 5 9 PERIMETER 8 18 F 5 17 DRGINDEX# 4 5 B - 21 DRGINDEX-ID 4 5 B - 25 OCODE 8 8 C - 33 MAPNAME 31 31 C - 64 USGS100 3 3 C - 67 USGS250 2 2 C - 69 CD 2 2 C - AREA: The area of the polygon in square coverage units. PERIMETER: The length of the polygon perimeter of the polygon in coverage units. DRGINDEX#: The software-assigned unique integer identification number. DRGINDEX-ID: A user-assigned identifier number. OCODE: USGS coding convention for 7.5 X 7.5 minute quads. MAPNAME: Name of 7.5 X 7.5 minute quad map. USGS100: Three character USGS code for 1 degree by 30 minute (100K) quad containing the polygon. USGS250: Two character USGS code for 2 degree by 1 degree (250K) quad containing the polygon. CD: CD number - index to which CD the image is on. DISPLAYING ADJACENT QUADS Though the quads have been trimmed to 7.5 minute neat lines, adjacent quads will still overlap due to "filler" pixels along the sides. These filler pixels are required because in an albers-based coordinate system the Y axis is parallel with true north only along the central meridian. Therefore, away from the central meridian the quads are canted with respect to the raster data structure and areas between the neatline and the edge of the data structure contain filler cells that overlap adjacent quads. Fortunately these filler cells have a unique color index of "0" that, depending on the display software being used can be set to transparent, allowing colors from adjacent quads to show through. Also, a raster-based GIS can be used to merge adjacent quads employing rules to ensure that index "0" never overwrites any other index. DATA CONTACT: Contact Name: Roger Ewers - Teale GIS Contact's Phone: 916-263-1488 DOCUMENTATION DATE: 12/15/1998