LIBRARY : <NONE>

LAYER NAME : <NONE>

NAME : DRG - Digital Raster Graphic

USGS 7.5' Quad Images (full sheet)

LOCATION : /drgcomp/q24k/(directory by degree block)

(Images are compressed with gzip)

COVERAGE DESCRIPTION:

Digital Raster Graphics are PackBit-compressed tiff images of USGS 7.5

minute quadrangle maps. There are 2,851 images covering the entire state

of California. Teale Data Center created the DRGs for California on behalf

of USGS. Teale's DRGs differ from those produced by USGS in terms of

resolution and projection.

BRIEF METHODOLOGY:

- Map is scanned at 400 dpi, and image colors normalized to 13 RGB values.

- Image is converted to Arc Info grid file

- Grid file undergoes descreening to enhance solid fill areas

- Grid file is registered to albers coordinate system.

- Grid file is converted to .tif image with PackBit compression option.

VITAL STATISTICS:

Resolution: 400 d.p.i., approximately 1.5 meters per pixel

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: None - public domain data

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, except for incomplete blocks along the state boundary.

DRG files are named according to USGS 'ocode' designation.

example: o35116a7.tif

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: o35116a7.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 image itself, and not

the latitude longitude values at the map corner. 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

DRG.DBF - dbase file that contains metadata for each quad. This file

is found on the metadata CD (#80).

DRG.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 3 3 C -

62 FILESIZE 2 2 I -

64 MAPSCALE 8 8 C -

72 FORMAT 20 20 C -

92 REF_CODE 25 25 C -

117 YEAR 4 4 C -

121 YRORIGMAP 4 4 C -

125 YRREVISION 4 4 C -

129 YRAIRPHOTO 4 4 C -

133 YRFIELDCK 4 4 C -

137 YRPHTOTOPO 4 4 C -

141 YRREVSOURC 4 4 C -

145 YRPHTOINSP 4 4 C -

149 LIBUPDATE 8 8 C -

157 SOUTH 8 10 F 5

165 NORTH 8 10 F 5

173 EAST 8 10 F 5

181 WEST 8 10 F 5

189 SE_COR_LON 9 9 C -

198 SE_COR_LAT 9 9 C -

207 CONTOURINT 10 10 C -

217 CONINTRMIT 10 10 C -

227 VERT_DATUM 15 15 C -

242 STATE1 2 2 C -

244 STATE2 2 2 C -

246 TYPE 1 1 C -

247 PROJECTION 80 80 C -

327 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 1:25,000 scale, 7.5 X 15 minute quad map

(see note below)

CD CD number - index to which CD the image is on

#32A and #32B replace #32 due to increased file size

of updated DRGs

FILESIZE Approximate size of tiff image file in megabytes.

Trimmed version images are about 10% smaller than

untrimmed.

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

LIBUPDATE Date (YYYYMMDD) of updated image replacement in Teale

library

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

(SOUTH, NORTH, EAST and WEST are used for trimming DRGs

to their neatline, or in the case of irregular DRGs, to

the outer extent of the map area.

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 (size) of map, to identify non-standard size 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 DRGs are images of 1:25,000 scale 7.5' x 15' USGS topo maps.

These USGS products were created in place of the 1:24,000 7.5 minute

format in limited areas of the United States, and each map sheet covers

an area equivalent to two adjacent 1:24,000 quads. These maps occur in

portions of Trinity, Shasta and Tehama counties, and one area on the

California-Nevada border. These DRGs are named according to their

1:24,000 map name. For example, ONO EAST (o40122d5) and ONO WEST

(o40122d6) are identical images of the ONO 7.5 X 15 Minute map.

FILENAME 1:24,000 MAP NAME 1:25,000 MAP NAME

o39119h8 SEVEN LAKES MOUNTAIN DOGSKIN MTN

o40122a7 SOUTH YOLLA BOLLY MOUNTAINS SOUTH YOLLA BOLLY

o40122a8 SOLOMON PEAK SOUTH YOLLA BOLLY

o40122b7 TOMHEAD MOUNTAIN NORTH YOLLA BOLLY

o40122b8 NORTH YOLLA BOLLY NORTH YOLLA BOLLY

o40122c5 CHICKABALLY MTN EAST CHICKABALLY MTN

o40122c6 CHICKABALLY MTN WEST CHICKABALLY MTN

o40122c7 BEEGUM BEEGUM

o40122c8 PLATINA BEEGUM

o40122d5 ONO EAST ONO

o40122d6 ONO WEST ONO

o40122d7 ARBUCKLE MOUNTAIN CHANCHELULLA PEAK

o40122d8 CHANCHELULLA PEAK CHANCHELULLA PEAK

o40123a1 WRIGHTS RIDGE FOUR CORNERS ROCK

o40123a2 FOUR CORNERS ROCK FOUR CORNERS ROCK

o40123b1 BLACK ROCK MOUNTAIN BLACK ROCK MTN

o40123b2 SWIM RIDGE BLACK ROCK MTN

o40123c1 PONY BUCK PEAK PONY BUCK PEAK

o40123c2 SMOKY CREEK PONY BUCK PEAK

o40123d1 WILDWOOD DUBAKELLA MTN

o40123d2 DUBAKELLA MOUNTAIN DUBAKELLA MTN

7 DRGs were scanned from quad maps that have NAD83 corners:

o38121e3 CARMICHAEL

o38121e6 DAVIS

o38121e7 MERRITT

o38121f3 CITRUS HTS

o38121f4 RIO LINDA

o38121g3 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.

DRGINDEX COVERAGE POLYGON ATTRIBUTES

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 3 3 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.

The file size of updated images for CD 32 where large

enough to necessitate the division of the area covered

by CD #32 into two, resulting in #32A (north), and #32B

(south).

DATA CONTACT:

Contact Name: Roger Ewers - Teale GIS

Contact's Phone: 916-263-1488