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